Cerrado, constituting native Brazilian vegetation in the tropical and subtropical grasslands, savannas, and shrublands biome, has been extensively replaced by crop and pastureland, resulting in reduced water recycling to the atmosphere via evapotranspiration (ET). Re-introducing trees via integrated land-use systems potentially restores soil health and water-related processes; however, field data are scarce. During two years, we monitored soil moisture dynamics of natural Cerrado (CER), continuous pasture (COP), integrated crop-livestock (ICL), and integrated crop-livestock-forestry (ICLF) systems across 100 cm soil depth. Across years, mean soil moisture was highest for ICL, followed by COP and lowest in systems with trees (ICLF and CER). However, seasonal and spatial analyses revealed pronounced differences between soil layers and systems. COP and ICL mainly lost water from upper soil layers, whereas in ICLF, the strongest water depletion was observed at 40–100 cm depth, almost reaching a permanent wilting point during the dry season. CER was driest in the upper 40 cm, but water storage was highest below 60 cm depth. Our results suggest that compared to conventional land-use practices, integrated systems, including trees, increase water recycling to the atmosphere via ET and potentially compensate for the loss of key ecological functions of degraded or replaced Cerrado.

AbstractMost of our insights on whole‐plant transpiration (E) are based on leaf‐chamber measurements using water vapor porometers, IRGAs, or flux measurements. Gravimetric methods are integrative, accurate, and a clear differentiation between evaporation and E can be made. Water vapor pressure deficit (VPD) is the driving force for E but assessing its impact has been evasive, due to confounding effects of other climate drivers. We developed a chamber‐based gravimetric method, in which whole plant response of E to VPD could be assessed, while keeping other environmental parameters at predetermined values. Stable VPD values (0.5–3.7 kPa) were attained within 5 min after changing flow settings and maintained for at least 45 min. Species differing in life form and photosynthetic metabolism were used. Typical runs covering the range of VPDs lasted up to 4 h, preventing acclimation responses or soilborne water deficit. Species‐specific responses of E to VPD could be identified, as well as differences in leaf conductance. The combined gravimetric‐chamber‐based system presented overcomes several limitations of previous gravimetric set ups in terms of replicability, time, and elucidation of the impact of specific environmental drivers on E, filling a methodological gap and widening our phenotyping capabilities.

Integrated-crop-livestock-forestry (ICLF) systems are currently promoted as a measure for sustainable intensification of agricultural production. However, due to complex interactions among ICLF components, we are still lacking evidence about the system’s resilience regarding water availability, especially for regions characterized by pronounced wet and dry seasons and frequent droughts. For a mature ICLF system in the Cerrado biome of central-west Brazil comprising rows of eucalyptus trees (Eucalyptus grandis x Eucalyptus urophylla, H13 clone) at a spacing of 22 m in combination with Brachiaria brizantha cv. BRS Piatã pasture we continuously measured soil moisture (SM) until 1 m depth and supported this data with measurements of photosynthetically active radiation (PAR) and aboveground green grass biomass (AGBM) across transects between the tree rows for almost two years. Across the seasons a distinct gradient was observed with SM being lower close to the tree rows than in the space between them. During winter SM decreased to critical values near the tree lines in the topsoil. During spring and summer, incident PAR was 72% and 86% lower close to the trees than at the center point. For autumn and winter PAR was more evenly distributed between the tree rows due to inclination with notably up to four times more radiation input near the tree lines compared to spring and summer. AGBM showed a clear distribution with maximum values in the center and about half of the biomass close to the tree rows. Our data suggest that, restrictions in AGBM accumulation shifted among seasons between water limitations in winter and light limitations during summer. Interestingly, SM changes during wetting and drying events were most pronounced in subsoils near the tree rows, while the topsoil showed much less fluctuations. The subsoil in central position showed the lowest SM dynamics in response to drought maintaining a relative high and constant SM content, therefore functioning as important water reservoirs likely improving the resilience of the system to drought stress. Results of this study could help to improve management and the design of ICLF systems in view of sustainability and resistance to (water) crises but should be further supported by in depth analysis of soil water dynamics as affected by climate gradients, soil types and different management practices.

Effects of Shading and Soil Moisture on Brachiaria brizantha Biomass in an Integrated Crop-Livestock-Forestry System SARAH GLATZLE1, MARCUS GIESE1, SABINE STÜRZ1, MARIANA PEREIRA1, ROBERTO G. ALMEIDA2, FOLKARD ASCH1 1University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Germany 2EMBRAPA Beef Cattle, Integrated Production Systems, Brazil Components of integrated production systems may compromise each other in competition for resources such as water and light. A smart and sustainable management of these resources is key to an overall successful system performance but often basic information are missing of how components and resources interact. This study analysed the seasonal dynamics of photosynthetically active radiation (PAR), soil moisture and grass biomass for integrated Crop-Livestock-Forestry (ICLF) demonstration plots in Campo Grande-MS, Brazil. Data were collected at three ICLF plots consisting of grass pasture (Brachiaria brizantha BRS cv. Piatã) lined with east-west orientated strips of 20m high Eucalyptus trees (Eucalyptus urograndis) in 22m distance. PAR (AccuPAR CP-80), soil moisture (DELTA T FDR) and grass biomass (moving cages) were sampled in each plot in a line of five sampling points between tree rows to represent the shading gradient. During rainy season (Dec–Feb) the PAR gradient was extremely high ranging from on average 1300 μmol m−2 s−1 (centre positions) to only 180 μmol m−2 s−1 near trees. In contrast due to lower inclination all points receive more or less the same amount of PAR (500 μmol m−2 s−1) during dry season (Jun–Aug). For soil moisture we measured a clear gradient from on average 29–32 Vol % at centre positions to 20– 25 Vol % near the tree lines. Dry season revealed same pattern with on average 3–5 Vol % lower values across the gradient. Biomass distribution showed a clear gradient as well with twice as much DM in centre positions for both seasons, while DM was about halved during dry season. Although we recorded a very high variation of PAR across the gradient between trees during rainy season, soil water content appears dominant affecting grass biomass growth according to correlation analysis. This relation was not surprisingly tightened during dry season when soil moisture contents approach wilting points more often. However, differences in energy budgets across the gradient and seasons resulting from radiation inputs are tremendous and should be considered in follow up analysis and management strategies of ICLF systems in relation to tree distances and height.

High impact grazing (HIG) was proposed as a management option to reduce standing dead biomass in Northern Argentinean (Chaco) rangelands. However, the effects of HIG on grassland diversity and shifts in plant functional groups are largely unknown but essential to assess the sustainability of the impact. During a two-year grazing experiment, HIG was applied every month to analyze the seasonal effects on plant species composition and plant functional groups. The results indicate that irrespective of the season in which HIG was applied, the diversity parameters were not negatively affected. Species richness, the Shannon–Wiener diversity index and the Shannon’s equitability index did not differ from the control site within a 12-month period after HIG. While plant functional groups of dicotyledonous and annual species could not benefit from the HIG disturbance, C3-, C4-monocotyledonous and perennials increased their absolute and relative green cover. Our results suggest that HIG, if not applied in shorter frequencies than a year, neither alters diversity nor shifts the plant species composition of the grassland plant community, but instead it promotes previously established rather competitive species. HIG could therefore contribute as an alternative management practice to the sustainable land use intensification of the “Gran Chaco” grassland ecosystem and even counteract the encroachment of “low value” species.

In this study we applied a landscape based soil-crop/tree integrative model (Land Use Change Impact Assessment, LUCIA) and investigated the efficacy of erosion control measures in rubber plantations under increased precipitation and temperature based on existing climate change scenarios. The model was firstly calibrated and validated at plot level to simulate weed management (“no-weeding”, “once-weeding”, “twice-weeding” and “clearweeding”) effects on soil loss in rubber plantations. Subsequently, the model was calibrated to simulate total sediment yield in a small watershed (.. ha, or km2) located in Xishuangbanna, South-West China, where rubber plantations occupy around 15 % land use in this watershed. Model outputs suggested that total soil loss in the watershed decreased by 15 % with reduced herbicide application in rubber plantations. Scenarios of climate change were further applied in the model to assess response of erosion control measures to increasing precipitation and temperature: 1) ‘baseline’ with rainfall and temperature measured in 2014; 2) ‘R+’ with rainfall amount increased by 2.6%; 3) ‘T+’ with temperature increased by 2.4◦C; 4) ‘RCP (representative concentration pathways) 8.5’ with rainfall increased by 2.6% as well as temperature by 2.4◦C. Modelling results indicated that increasing temperature (‘T+’) decreased soil litter cover by accelerating decomposition. This affected soil loss to higher extent than increasing rainfall (‘R+’) at both plot and watershed level. Soil loss in rubber plantation increased from 2 t ha−1 to 3 t ha−1 under “twice-weeding” due to increasing precipitation and temperature; while reduced herbicide application (“noweeding” and “once-weeding”) kept soil loss below 1 t ha−1. Total sediment yield in the watershed increased from 800 t a−1 to 1130 t a−1 by increased precipitation and temperature under current management but was reduced 960 t a−1 under reduced herbicide in rubber plantations. The results of this study suggest that management has the potential to mitigate soil loss by climate variability or change.

Rubber plantations are strongly increasing in Xishuangbanna, Southwest China. Herbicide applications controlling the undergrowth may increase erosion potential and carbon export by decreasing plant and litter cover. Quantitative evaluation of the erodibility of rubber systems and the impact of herbicides has not been studied. This study aimed at assessing the impact of herbicide application on soil loss and the induced carbon export in a rubber plantation. Runoff, sediment yield, and total organic carbon (TOC) content in sediments were measured under natural rainfall for one year in a 12-year old rubber plantation subjected to three different herbicide treatments: i) standard application twice per year practiced by the majority of farmers (Hs); (ii) no application to maintain a high understory plant cover (H−); and (iii) bimonthly application (adopted by some farmers) in order to largely avoid understory plant cover (H+). The infiltration rate under different treatments was measured with a rainfall simulator. Monthly measurements of fine root density using soil coring, surface cover, and understory plant cover making photography were carried out. The highest soil and TOC in sediment losses (425gm−2, 15gCm−2 respectively) were observed under H+ treatment, while under H− treatment they were strongly reduced (50gm−2 and 2gCm−2 respectively). Compared to Hs, H+ increased soil and sediment TOC loss by 34 and 52%, while H− reduced soil and TOC loss, both by 82%. Notably, H− presented high conservation efficiency, reducing sediment yields by 86% for highly erosive rainfall events. The cover and management (C) factor and support practice factor (P) are essential components of the common Universal Soil Loss Equation (USLE) model. We combined the C and P factors into a single value (CP) and, for the first time, derived estimations of annual CP values for a rubber plantation (0.005–0.04) using our data. The dynamic change of the CP factor of plantations during the rainy season was quantified by relating relative soil loss to changes in understory plant cover (PC), which can be expressed as CP=0.04e−0.028PC (R2=0.88, P<0.0001). Understory plant cover as affected by herbicide application was thus a key factor controlling the soil loss of established rubber systems. This suggests options to improve the soil conservation and biodiversity through reduced herbicide management.

Topography has strong effects on microclimates; thus may influence the decomposition of organic matter, a key process determines soil nutrient availability and carbon fluxes in terrestrial ecosystems. Yet, little is known if and how topographic factors influence litter decomposition. We studied the effects of slope aspect (south- vs. north-facing slopes) and position (base and middle positions) on plant shoot litter and root decomposition. We analyzed dynamics of litter mass loss in a 442-day period, and soil and vegetation characteristics in a typical semiarid hilly grassland. Our results showed that the decomposition of roots was faster at south-facing than at north-facing sites, which can be explained by the 2°C higher soil temperature at south-facing sites. Decomposition rate of shoot litter were not different between slope aspects. North-facing sites had 76% higher aboveground biomass and 80% higher belowground biomass than those at south-facing sites. Accordingly, plant N and C storages at north-facing sites were 67% and 76% higher than those at south-facing sites, respectively. The smaller plant carbon and nitrogen stocks and the faster root decomposition at south-facing slopes suggest higher proportions of plant C and N are lost from the ecosystem than that at north-facing slopes. This work highlights the necessity of taking slope aspect into account in carbon and nitrogen cycling studies in hilly grasslands.

From 2004 to 2010, the Sino-German research group MAGIM (Matter fluxes of Grasslands in Inner Mongolia as affected by grazing) ran a grazing experiment in a typical steppe ecosystem in Inner Mongolia, North China. Multiple ecological effects of grazing, climate variability and topography on plant and animal productivity, plant species composition change, decomposition and mineralization, soil nitrogen and organic matter distributions and dynamics, soil physics and chemistry, and soil-atmosphere gas exchange were measured in fenced plots with defined stocking rates and under different grazing management systems. This paper reviews and synthesizes the most important outcomes, conclusions, and open questions from the different project groups, as published in 125 ISI articles.While greenhouse gas fluxes, plant properties, and livestock performance were particularly responsive to (inter-) annual climate variability, soil properties were more affected by grazing intensity. Various management options based on the project results for semi-arid grasslands under changing climatic conditions are discussed. (C) 2016 Elsevier Ltd. All rights reserved.

The humid subtropical climate of central west Brazil mostly provides sufficient rainfall and adequate temperatures to support year-round agriculture production in integrated tree-crop-livestock production systems. However, high rainfall variability during the drier winter is increasingly compromising one of the most productive agricultural regions in Brazil. In addition, climate scenarios indicate up to 30 % less rainfall during winter and increasing frequency of dry periods for central-south Brazil within the forthcoming decades. Information focusing on plant water use dynamics of intergrated crop-livestock-forestry systems is rare and insufficient to estimate the system’s adaptive capacity to temporal water limitations and climate variability or change. The objective of this research is to characterise whole plant transpiration of selected common cultivated fodder grasses in response to atmospheric drought and shading. Whole plant transpiration rates [mmol m−2 s−1] of the fodder grasses Brachiaria brizantha cv. Marandu, Brachiaria humidicola cv. Llanero, Brachiaria decumbens, Brachiaria ruziziensis, Panicum maximum cv. Mombaca and Panicum maximum cv. Tanzania was measured in a transpiration chamber with adjustable atmospheric vapour pressure deficits (VPD) and three different radiation intensities (420 μmol m−2 s−1, 730 μmol m−2 s−1, 1200 μmol m−2 s−1). The results show that with increasing vapour pressure deficit and radiation intensity the transpiration rates for each fodder grass species increased linear but with different slopes. While under low VPD levels the radiation impact on transpiration rates was rather small, the effect was considerably increased under high VPD levels. Our results suggest that common cultivated fodder grasses in Brazilian pastures reveal different response dynamics to light intensity and VPD. Both abiotic factors are highly variable within integrative crop-livestck forestry systems and improved understanding of the plant’s water use traits will contribute to a resource use efficient, climate smart, and sustainable land use management.

Grasslands are the main source of feed for cattle in Argentina. Standing dead biomass accumulation threatens efficient resource use. The effect and timing of high impact grazing by cattle as a management tool to remove excess standing dead biomass was studied in grasslands of North Eastern Argentina. High impact grazing (HIG) was introduced monthly on adjacent paddocks over the course of the year and its effects were studied for 12 months following the treatment. Dynamics of biomass re-growth and accumulation of green and standing dead biomass were studied. HIG generally improved the green to total biomass ratio and reduced the overall biomass in the paddocks. Strong seasonal dynamics in the biomass growth rates strongly influenced the effects of timing of the HIG. All sub-plots subjected to HIG showed a growth pattern anti-cyclic to control, with an active growth phase during autumn when the biomass in the control sub-plots decreased. Best results in terms of standing dead biomass reduction and dead to green biomass ratios were achieved after HIG in winter. HIG in autumn, however, reduced fodder availability and reduced next year's grassland's productivity. We propose strategically (carefully) timed HIG not only as an alternative method to reduce standing dead biomass, but also as a pathway to sustainable intensification by providing green forage at levels equal or even higher than those achieved under continuous traditional grazing. (C) 2015 Elsevier Ltd. All rights reserved.

Many uncertainties exist concerning the quantification of the carbon sequestration potential in savannah ecosystems. Biomass and carbon pools are highly variable within the different vegetation types of this zonal ecosystem, and very often most basic and sufficient accurate information related to biomass dynamics are not available. Here we present a methodological non-destructive approach to determine high-resolution data of leaf area index (LAI) and above-ground biomass (AGB) from a thorn-shrub savannah ecosystem in southern Ethiopia, representative for the African Sahel-Zone with bimodal rainfall distribution. Optical and destructive LAI measurements were taken from 5 dominant shrub and tree species in weekly intervals during one rainy season. We correlated the results of multiple biomass harvestings with the non-destructive optical method. Multiple optical LAI measurements performed in different horizontal vegetation layers at a 5 m grid allowed us to upscale LAI and biomass information collected at the species to the plot level of the shrubtree formations. Established allometric equations for above-ground biomass estimations of dominant shrub and tree species were additionally used to validate our method. We discuss our results towards the option to use this optical method for estimating aboveground net primary production (ANPP) and, thus, the carbon sequestration potential for shrub-tree dominated savannah ecosystems. The results indicated that spatial and temporal biomass heterogeneity at species and plot level resulting from the system’s high natural variability will be the main methodological challenge to cope with. Consequently, optical biomass monitoring will be a key-method to determine the spatial and temporal variability of ANPP from tree and shrub dominated savannah ecosystems and should therefore be subjected to a scientific discussion as promising approach to estimate the carbon sequestration potential of this major tropical ecosystem.

The Borana rangelands in southern Ethiopia used to be among the most productive pastoral areas in East Africa. However, over-utilisation and over-grazing have resulted in declining rangeland conditions and woody-species encroachment. Payment for environmental services (PES) based on carbon sequestration has been proposed as additional livelihood option to offer an incentive for an improved and sustainable management which in turn is expected to increase the carbon sink in such semi-arid ecosystems. Nevertheless, information on basic aboveand below-ground biomass and carbon pool inventories providing reference data for common vegetation types of the Borana rangelands is missing. Within four representative vegetation types (grassland (GL), tree savannah (TS), bush-tree savannah (BT) and bushland (BL)), we repeatedly determined aboveand below-ground biomass (AGB, BGB) using destructive sampling methods and allometric equations (for woody biomass). Total mean AGB (herbaceous + woody biomass) was highest in TS (24.2 ± 7.6 t ha−1) and lowest in GL (1.0 ± 0.4 t ha−1). Regarding the sum of all herbaceous biomass fractions (green, standing dead, litter), AGB decreased from 1.94 t ha−1 (BL) to 1.02 t ha−1 (GL) in June 2012 (after the rain season) and from 2.83 t ha−1 (BL) to 0.30 t ha−1 (GL) in Oct. 2012 (after the dry season). In contrast, below-ground biomass (BGB) of the herbaceous layer ranged from 3.20 t ha−1 (BT) to 2.45 t ha−1 (GL) and did not show this pattern among vegetation types. Dynamic sampling indicates AGB minima before and maxima after the rainy season, but only for the vegetation types GL and BT, while BL and TS did not show a pronounced seasonal dynamic. Our data provide a first multi-seasonal quantification of aboveand below-ground biomass and carbon stock estimates for common vegetation types in the Borana rangelands. We hypothesise that differences in biomass and carbon pools of the herbaceous layer between vegetation types are mainly based on above-ground vegetation dynamics, while below-ground biomass allocation does not reflect the above-ground pools. Thus, a first step to building a database as reference for PES systems and sustainable rangeland management has been taken.

The analyses of plant leaf traits that strongly influence aboveground net primary production (ANPP) are indispensable for understanding the process of plant biomass formation. However, there are few studies that have attempted to relate patterns of ANPP under contrasting management practices to plant leaf-level traits. To assess how leaf traits affect plant biomass accumulation under different land-use practices, we examined leaf traits and biomass production in three differently managed sites in the Inner Mongolia steppe: a site fenced since 1979 (UG), a winter grazing site (WG), and a heavily grazed site (HG). Low soil water content, leaf area index, and potential growth ability of species at site HG led to low crop growth rate (CGR), net assimilation rate (NAR), and relative growth rate (RGR); resulting in lower ANPP as compared to sites WG and UG. Irrespective of land-use management, prolonged drought significantly decreases ANPP even though it systematically increases mean CGR and RGR. However, leaf N content and leaf weight ratio are the crucial components necessary to determine the RGR at site WG. This suggests that low leaf N and availability of soil N due to haymaking may be responsible for neither over-compensatory nor compensatory growth in this site. The low ANPP in dry years is not due to the low mean CGR and RGR but rather to the short effective growing days (referring to the days the vegetation actually grows), suggesting that production-adjusted grazing regimes may be the most suitable measures for precision land management and avoiding grassland degradation.

Water use efficiency (WUE) is a key indicator to assess ecosystem adaptation to water stress. Rain use efficiency (RUE) is usually used as a proxy for WUE due to lack of transpiration data. Furthermore, RUE based on aboveground primary productivity (RUEANPP) is used to evaluate whole plant water use because root production data is often missing as well. However, it is controversial as to whether RUE is a reliable parameter to elucidate transpiration efficiency (TE), and whether RUEANPP is a suitable proxy for RUE of the whole plant basis. The experiment was conducted at three differently managed sites in the Inner Mongolia steppe: a site fenced since 1979 (UG79), a winter grazing site (WG) and a heavily grazed site (HG). Site HG had consistent lowest RUEANPP and RUE based on total net primary productivity (RUENPP). RUEANPP is a relatively good proxy at sites UG79 and WG, but less reliable for site HG. Similarly, RUEANPP is good predictor of transpiration efficiency based on aboveground net primary productivity (TEANPP) at sites UG79 and WG but not for site HG. However, if total net primary productivity is considered, RUENPP is good predictor of transpiration efficiency based on total net primary productivity (TENPP) for all sites. Although our measurements indicate decreased plant transpiration and consequentially decreasing RUE under heavy grazing, productivity was relatively compensated for with a higher TE. This offset between RUE and TE was even enhanced under water limited conditions and more evident when belowground net primary productivity (BNNP) was included. These findings suggest that BNPP should be considered when studies fucus on WUE of more intensively used grasslands. The consideration of the whole plant perspective and "real" WUE would partially revise our picture of system performance and therefore might affect the discussion on the C-sequestration and resilience potential of ecosystems.

In temperate grasslands, the belowground system is the central part of carbon allocation and cycle. Belowground primary productivity (BNPP) and root turnover are important indicators of ecological properties of this ecosystem, such as carbon cycle and balance. Songnen grassland is located in north-eastern part of China, and the livestock grazing has been considered as one of the important land-use regimes. This area is under an increasing pressure of degradation as a result of the rising demand for natural resources and animal products. Much of previous studies have only focused on the effects of grazing intensity on aboveground production. However, little is known about the influences of different grazers on BNPP and root turnover. Based on the different grazers, four treatments were established, including cattle grazing, sheep grazing, mixed cattle and sheep grazing and control without grazing. BNPP and root turnover were measured by Ingrowth Donuts method and the improved root window method, respectively. The highest value of BNPP was found under sheep grazing followed by cattle grazing and mixed grazing. Un-grazed treatment showed the lowest value of BNPP. Similarly, root turnover was faster under grazing condition than the un-grazed treatment, especially in the cattle grazing treatment. The differences in BNPP observed among grazing treatments can be explained by selective herbivory of different grazers. Furthermore, BNPP and the proportion of root cohort surviving are positively correlated to soil moisture, suggesting soil water availability is an overriding factor controlling the formation of belowground net primary production and root turnover. Positive relationship between BNPP and root turnover indicates that high BNPP under grazing condition may facilitate root replacement, thus increase soil C sequestration.

High altitude upland rice (Cluza sativa L)production systems are expected to benefit from climate change induced increase in temperatures. The potential yield of rice genotypes is governed by the thermal environment experienced during crop development phases when yield components are determined. Thus, knowledge on genotypic variability in phenotypic responses to variable temperature is required for assessing the adaptability of rice production to changing climate. Although, several crop models are available for this task, genotypic thermal constants used to simulate crop phenology vary strongly among the models and are under debate. Therefore, we conducted field trials with ten contrasting upland rice (O. sativa L.) genotypes on three locations along an altitudinal gradient with five monthly staggered sowing dates for two years in Madagascar with the aim to study phenological responses at different temperature regimes. We found that, crop duration is equally influenced by genotype selection, sowing date and year in the high altitude. In contrast, in mid altitudes genotype has no effect on crop duration. At low altitudes crop duration is more affected by sowing date. Grain yield is strongly affected by low temperatures at high altitudes and severly influenced by frequent tropical cyclones at low altitudes. In high altitude, genotype explained 68% of variation in spikelet sterility, whereas in mid and low altitudes environment explained more than 70% of the variation. The phenological responses determining crop duration and yield, the basic genotypic thermal constants, and the analyses of genotypic thermal responses with regard to spikelet sterility reported here, provide valuable information for the improvement of rice phenological models urgently needed to develop new genotypes and better adapted cropping calendars. (C) 2013 Elsevier B.V. All rights reserved.

Medicago sativa is perennial forage with high yield and good quality. Plants growing in arid and semi-arid regions are often subjected to soil and atmospheric water deficit as well as high soil salinity during their life cycles. Plant transpiration increases at elevated atmospheric vapour pressure deficit (VPD), C3 species are reported to have a breakpoint (BP), above which stomatal conductance declines and limits transpiration rate to a maximum. Soil salinity is likely to be involved in transpiration response by affecting root hydraulic resistance, leaf water potential and stomatal conductance in salt-treated plants. The objective of this study was to compare the transpiration response of Medicago sativa over a range of VPD at various salt concentrations to identify the tolerance mechanisms to confront atmospheric water vapour deficit and salinity. Seeds of Medicago sativa were cultivated in a greenhouse till 8 weeks old and subjected to five salt treatments of 0, 40, 80, 120, 160 mM (NaCl :Na2SO4 = 1:1) for 14 days. Then plants were exposed to increasing VPD (0.5, 1.0, 1.5, 2.5, 3.5 kPa) in a controlled environment chamber. Leaf area ratio (LAR) and specific leaf area (SLA) significantly decreased at 80 mM and higher salt treatment, meaning Medicago sativa developed leaf thickness with increasing salinity at the expense of leaf area per plant. Total biomass was significantly reduced by salt stress but slightly changed when salt concentration exceeded 80 mM. Transpiration rate (TR) in control plants increased linearly with VPD up to 1.0 kPa, above which TR declined markedly. Salt treatment increased BP along the salt concentration gradient to 2.0 kPa at 160 mM, reflecting a compromised sensitivity in stomatal regulation. Increasing salt levels resulted in stomatal closure and consistent decrease of whole-plant transpiration rate. The results suggest that Medicago sativa down-regulates transpiration rate to conserve soil water, while reduction of SLA is assumed to compensate for decreased CO2 diffusion. Medicago sativa can effectively counteract negative effects of salinity and varying VPD in a semi-arid environment.