There are significant differences in the morphological and physiological responses of larch species with contrasting growth rates under fertilization. However, little is known about species-specific differences in responses to nutrient imbalance caused by fertilization. Therefore, in this study, the effects of nitrogen (N) and phosphorus (P) fertilization on the morphological, physiological and chloroplast ultrastructural traits of two contrasting larch species, fast-growing Larix kaempferi and slowly-growing L. olgensis, grown in larch plantation soil, were investigated during two growth seasons. It was shown that N and combined N and P (NP) fertilization increased plant photosynthesis, foliar N contents, chlorophyll contents, and dry mass accumulation and partitioning in aboveground organs in both larch species. Although P fertilization enhanced P accumulation, its presence reduced the N content in soluble proteins in the foliage of both larch species. Yet, P fertilization exhibited some differences in the two species: P fertilization increased photosynthesis, chlorophyll content and biomass accumulation of L. olgensis, while it decreased these parameters dramatically in L. kaempfert P fertilization increased foliar N content in L. olgensis, while it reduced it in L. kaempferi. P fertilized L. kaempferi had more damaged chloroplast ultrastructure than L. olgensis. In addition, L. kaempferi exhibited lower acid phosphatase activities, and higher photosynthesis and biomass accumulation than L. olgensis, except under P fertilization. L. kaempferi allocated more biomass into needles, except under P fertilization, while L. olgensis allocated more into stems under fertilization. In conclusion, it was shown that nutrient imbalance caused by P fertilization has greater negative effects on a fast-growing species than on a slowly-growing one, and the negative effects are related to differences in acclimation strategies, N partitioning to photosynthetic components, and P transportation and metabolism in the foliage.

Populus cathayana was employed as a model species to study sexual differences in plant growth, physiological, biochemical, and ultrastructural responses to manganese (Mn) stress with two different nitrogen sources (NH4 + and NO3 −). Results showed that NH4 +-N (3.75 mM) and NO3 −-N (3.75 mM) significantly increased plant growth, gas exchange capacity, as well as superoxide dismutase (SOD) and peroxidase (POD) activities in the leaves of both male and female P. cathayana. In addition, NH4 +-N supply could improve tolerance to Mn stress in both male and female P. cathayana with higher photosynthetic capabilities, biomass accumulation, antioxidant enzyme activities, superoxide radicals (O2 −) and thiobarbituric acid-reactive substances (TBARS) in leaves. Under the same condition, female plants grown under NO3 − supply exhibited significantly lower biomass accumulation, photosynthetic capabilities, and antioxidant enzyme activities than male plants because of higher Mn accumulation in both above- and belowground organs and higher ROS releasing rate in leaves. Moreover, damage to cellular ultrastructure was also observed in leaves of males and females exposed to Mn stress, but more strongly in females, with more visible degradation of mitochondrion in plant leave cells. The difference in the preferences for different N sources between male and female P. cathayana under Mn stress provides important guidance in fertilizing strategy to minimise intraspecific competition between female and male plants.

Recent studies have demonstrated that plants can determine the identity of neighbouring roots (e.g., self and non-self, kin and non-kin), but whether they can discriminate by sex remains an open question. Here, we predict that dioecious plants can modulate their root performance in response to local root conditions related to sex. Female and male Populus cathayana cuttings were planted in a greenhouse in root-owner (one individual without a root neighbour) or root-sharer pairs (two individuals with roots neighbouring each other) with equal amounts of nutrients and space per plant in three combinations (females-females, males-males or females-males); root morphology, biomass and allocation were investigated. P. cathayana root-sharers altered their root growth in same-sex but not in different-sex combinations. Females enhanced root growth and allocation but decreased root proliferation (greater diameter with reduced branching and specific root length) in the presence of a female root neighbour, while males reduced root growth but increased root morphological proliferation in contact with another male. Therefore, the effect of a neighbour of the same sex differed from that of a neighbour of the opposite sex, which suggests that these plants can recognize the sexual identity of their neighbours.

Non-structural carbohydrates (NSC) are critical to plant signaling, gene transcription, physiological processes, survival and growth. Previous studies have demonstrated that species differing in NSC contents have various responses to stressful environments. However, effects of intra- and interspecific competition or N fertilization on NSC have not been previously studied. We employed two coniferous tree species, Larix kaempferi and Larix olgensis, to investigate the effects of intra- and interspecific competition on NSC under two N supply levels, with and without N fertilization. N fertilization significantly promoted the growth rates, biomass accumulation, carbon isotope composition and N concentration of leaves of the two species. Competition patterns significantly affected the average root diameter. Interspecific competition tended to increase the specific root length and specific root tip density. Also, interspecific competition significantly increased the N concentration of leaves but declined their C:N ratio under no N fertilization (N) treatments. L. kaempferi greatly benefited from the presence of L. olgensis, particularly under N fertilization (N+) treatments. Competition patterns, N fertilization and their interactions promoted N and carbohydrate storage. Our results demonstrated that N was a crucial factor to drive and regulate carbon balance. Differences between species in carbohydrate metabolism may contribute to their coexistence or niche differentiation. (C) 2016 Elsevier B.V. All rights reserved.

To investigate how nitrogen (N) and phosphorus (P) fertilization affect plant growth, biomass accumulation and allocation, leaf N and P concentration, and also eco-physiological responses of Larix species with contrasting growth characteristics, slow growing (L. olgensis) and fast growing (L. kaempferi) saplings grown in larch plantation soil were exposed to different N and P regimes. The results showed that N and combined N and P (NP) fertilization promoted growth with a higher biomass accumulation, height growth rate (GR(H)), net photosynthesis rated (P-n), and photosynthetic P-use efficiency (PPUE) in both species, while P fertilization alone had a positive effect on the growth of L. olgensis but a negative effect on that of L. kaempferi. Moreover, N and NP fertilization increased the photosynthetic N -use efficiency (PNUE) of L. olgensis, while all fertilization treatments decreased that of L. kaempferi. Furthermore, P fertilization increased the N concentration of L. olgensis leaves but had no influence on that of L. kaempferi leaves, while it decreased the NSC concentration of L. olgensis leaves but stimulated the accumulation of starch, fructose and NSC in L kaempferi leaves. In addition, L kaempferi with higher GRH showed a greater biomass accumulation, growth, P-n, PNUE, and PPUE when compared to L. olgensis, except for biomass and PPUE under P fertilization and PNUE under N fertilization. These results indicated that the N and P balance rather than the absolute amount of them enhances the growth of L. kaempferi effectively, and P fertilization affects the morphological and physiological traits of the two larch species differently. We propose that the distinct effects of P fertilization on the two larch species were related to different regulation effects of P fertilization on the N concentration, and on the accumulation and transportation of photosynthetic products. (C) 2016 Elsevier B.V. All rights reserved.

The degree to which branches are autonomous in their acclimation responses to alteration in light environment is still poorly understood. We investigated the effects of shading of the sapling crown of Cunninghamia lanceolata (Lamb.) Hook on the whole-tree and mid-crown branch growth and current-year foliage structure and physiology. Four treatments providing 0, 50, 75 and 90% shading compared with full daylight (denoted as Treatment(0), Treatment(50%), Treatment(75%) and Treatment(90%), and Shaded(0), Shaded(50%), Shaded(75%) and Shaded(90%) for the shaded branches and Sunlit(0), Sunlit(50%), Sunlit(75%) and Sunlit(90%) for the opposite sunlit branches under natural light conditions, respectively), were applied over two consecutive growing seasons. Shading treatments decreased the growth of basal stem diameter, leaf dry mass per unit leaf area, stomatal conductance, transpiration rate, the ratio of water-soluble to structural leaf nitrogen content, photosynthetic nitrogen-use efficiency and instantaneous and long-term (estimated from carbon isotope composition) water-use efficiency in shaded branches. Differences between shaded and sunlit branches increased with increasing severity and duration of shading. A non-autonomous, partly compensatory behavior of non-shaded branches was observed for most traits, thus reflecting the dependence between the traits of sunlit branches and the severity of shading of the opposite crown half. The results collectively indicated that tree growth and branch and leaf acclimation responses of C. lanceolata are not only affected by the local light environment, but also by relative within-crown light conditions. We argue that such a non-autonomous branch response to changes in light conditions can improve whole-tree resource optimization. These results contribute to better understanding of tree growth and utilization of water and nitrogen under heterogeneous light conditions within tree canopies.

Female cuttings of Populus deltoides were sensitive to inorganic nitrogen forms and biased for NO 3 − –N, whereas males exhibited no obvious preference for nitrogen form in nitrogen fertilizations.

This paper studied the sex-specific differences of male and female Populus cathayana seedlings in their ecophysiological characteristics and photosynthesis under the stress of aluminum (216 mg Al(3+) x kg(-1)). Under the effects of aluminum, the malonaldehyde (MDA) and soluble protein (Pr) contents of the male and female seedlings increased significantly (P < 0.001), and the males had a significantly lower MDA content and a significantly higher Pr content than the females. The peroxidase (POD) activity of the males increased but the superoxide dismutase (SOD) activity decreased significantly, while the POD and SOD activities of the females had no significant variation. The net photosynthetic rate (Pn) of both male and female seedlings decreased significantly (P = 0.001), and the transpiration rate (Tr) of the female seedlings decreased (P = 0.007) and the instant water use efficiency (WUEi) increased significantly, while no significant variations were observed in the Tr and WUEi of the male seedlings. The total chlorophyll and chlorophyll a contents and chlorophyll a/b ratio of the females decreased significantly, resulting in a significantly higher chlorophyll a/b ratio of the males. The specific leaf area (SLA) of the females decreased but that of the males increased significantly. No significant variation was observed on the leaf- and stem dry mass. Comparing with the females, the males had higher Pr and chlorophyll contents and higher active antioxidant enzymes activity to maintain higher Pn, and thus, had greater resistance against aluminum stress.