ABSTRACT Predicting boreal forest growth is hindered by limited experimental tests on the compounding effects of climate change and atmospheric CO 2 . We integrated regional tree‐ring data with a peatland warming and CO 2 manipulation experiment, including 45 trait measurements, to assess growth responses of two widespread boreal conifers, Larix laricina and Picea mariana , to temperature, vapor pressure deficit (VPD), soil moisture, and elevated CO 2 . L. laricina growth was consistently more climate‐sensitive than P. mariana , increasing strongly with soil moisture and declining slightly with VPD at the regional scale, but responding positively to VPD and temperature—not soil moisture or CO 2 —at the experimental peatland. L. laricina 's acquisitive strategy enhanced water and nutrient uptake, sustaining growth but reducing hydraulic safety. By contrast, P. mariana 's conservative strategy maintained water‐use efficiency and hydraulic resilience without compromising growth. Our results challenge projections of widespread CO 2 fertilization in boreal forests and highlight conservative conifers as potential winners under warming and drying, sustaining growth while maintaining low mortality risk. This dynamic could reshape projections of the boreal carbon sink and its role in global climate feedback.
ABSTRACT The accumulation of microplastics (MPs) in soils worldwide has raised concerns about their potential impacts on microbially mediated carbon (C) and nitrogen (N) cycling. However, whether biodegradable and non‐biodegradable MPs differently affect microbial C and N metabolism and coupling, and whether these responses are modulated by co‐occurring plant identity remain uncertain. We combined a meta‐analysis with a controlled pot experiment comparing soil responses under two congeneric plant species exposed to two biodegradable and two non‐biodegradable MPs at doses ranging from 0% to 2% (w/w). In the meta‐analysis, MPs generally increased CO 2 emission and microbial biomass N (MBN), but had no significant overall effect on microbial biomass C (MBC). In the pot experiment, MPs likewise increased CO 2 emission, whereas overall effect sizes of MBC and MBN were nonsignificant. Nevertheless, these overall responses did not capture the distinct patterns of microbial C–N metabolic coordination between MP types. Under biodegradable MPs, tighter MBC–MBN coupling with a dose‐dependent shift toward greater respiratory C loss relative to MBC collectively indicated a maintenance‐associated metabolic pattern. In contrast, MBC–MBN decoupling and stronger MBC–CO 2 coupling under non‐biodegradable MPs indicated a biomass‐linked metabolic pattern. In addition, plant identity modulated these microbial metabolisms in an MP‐type manner, particularly in N‐related processes. These metabolic responses were accompanied with changes in soil property conditions and substrate availability, weakened DOC–DON coupling, and shifts in microbial community structure and life history strategy. RDA‐based hierarchical and variation partitioning and SEM further indicated that modeled soil property pathways were more prominent under non‐biodegradable MPs, while substrate‐related pathways were prominent under biodegradable MPs. Together, the meta‐analysis reveals the general microbial metabolic patterns under MP type, and the pot experiment further reveals how MP type and plant identity jointly influence microbial C–N metabolism through contrasting associations with soil substrates and property conditions.
ABSTRACT Ecological restoration is widely expected to recover multiple ecosystem attributes, yet biological structure and ecosystem functioning may respond differently to hydromorphological restoration. Interpreting functional change is further complicated because higher or lower process rates do not inherently indicate recovery; their ecological meaning depends on how degraded and restored conditions compare with an appropriate reference state. We synthesised 582 effect sizes from 66 studies to quantify responses of nine ecosystem functions to hydromorphological restoration of streams and to assess whether changes in biological structure coincided with functional responses. Ecosystem‐function responses varied substantially among processes and baselines. Gross primary production was significantly higher in degraded than in reference streams, illustrating that elevated functional rates do not necessarily indicate reference‐like ecological conditions. Restoration did not consistently reverse degradation‐associated functional differences: denitrification was significantly lower in restored than in degraded streams, whereas nitrate uptake remained significantly lower in restored than in reference streams. Other restored–reference differences were generally weak or uncertain. Functional responses did not differ systematically among broad restoration‐measure categories. Restoration age was associated with changes in gross primary production and denitrification relative to degraded conditions, but none of the functions showed detectable convergence towards or divergence from reference conditions through time. In studies measuring both biological structure and ecosystem functioning, biological responses to restoration were generally positive relative to degraded conditions, whereas functional responses were more variable. However, the available evidence was too uncertain to conclude that biological and functional responses systematically differed. Our synthesis shows that functional recovery cannot be inferred either from restoration‐associated change alone or from concurrent biological recovery. Assessing restoration success therefore requires direct measurements of ecosystem processes and ecologically meaningful reference conditions that reveal whether functional change represents movement towards a process‐specific restoration target.
ABSTRACT Alpine ecosystems are experiencing warming, leading to alpine greening—an upward migration and enhanced productivity of vegetation. Although soils represent the largest carbon (C) stocks in these ecosystems, impacts of greening on soil organic carbon (SOC) dynamics remain unknown, especially in the high alpine zone. We measured SOC stocks, quality and radiocarbon ( 14 C) based turnover rates along elevation gradients from (sub)alpine forests to periglacial zones on three bedrock types, representing trajectories of changes in climate and vegetation and weathering regime. Data were linked to SOC stabilizing pedogenic oxides (PO) to assess the potential of soils to sequester C upon alpine greening. Results show pronounced decreases in SOC stocks (from 10 to 1 kg C m −2 ) and increases in 14 C‐based turnover times (from decades to millennia) with increasing elevation. This pattern followed a non‐linear sigmoidal function with a threshold at the vegetation line where grassland transitions to the nival zone. High alpine soils showed low SOC:PO ratios, indicating low C saturation and a high capacity to stabilize SOC on reactive minerals. However, negligible 14 C‐derived carbon inputs suggest that low vegetation productivity constrains SOC sequestration in these soils. In contrast, towards lower elevation with a warmer climate, grassland soils receive higher C inputs, but appear more C saturated, leading to greater SOC turnover but little SOC stock changes. Bedrock influenced SOC dynamics with approximately 50% smaller SOC stocks and faster turnover rates in dolomitic than in siliceous soils, due to slower weathering and lower SOC stabilization. Using elevation as a space‐for‐time substitution, we infer that SOC sequestration under alpine greening will be confined to areas around the vegetation line, with parent material influencing the magnitude of C uptake. Future projections of SOC dynamics should account for vegetation shifts and bedrock‐driven stabilization to constrain the role of alpine soils in land carbon‐climate feedbacks.
ABSTRACT Understanding how climate shapes ecosystem productivity through energetic constraints and changes in the functional properties expressed by vegetation remains challenging. This is central to trait‐based biodiversity–ecosystem functioning research in mountain grasslands where warming and environmental gradients interact. Here, we distinguish direct climatic controls on productivity from indirect pathways operating through changes in canopy functional composition, physiological state, and within‐plot spectral functional heterogeneity across the European Alps. Using Sentinel‐2 time series (2017–2024), we quantified canopy functional structure from spectral proxies of pigment investment and water status, within‐plot spectral functional heterogeneity using the functional richness (FRic) metric, and vegetation productivity using near‐infrared reflectance of vegetation (NIRv). We combined panel‐data models with piecewise structural equation modeling to partition climate associations into direct and trait‐mediated components operating through canopy functional properties and used varying‐coefficient models to evaluate how these pathways vary along environmental gradients. We identified two pathways linking climate to productivity. Warmer growing seasons increased productivity directly but were associated with a lower chlorophyll‐to‐carotenoid pigment balance, consistent with greater relative carotenoid investment, generating an opposing indirect pathway. Greater winter snow accumulation reduced productivity primarily through a direct pathway, while its canopy‐mediated pathways were uncertain. Climatic water deficit reduced canopy water status and within‐plot spectral functional heterogeneity, but its direct and total associations with productivity were not distinguishable from zero. Environmental context modulated climate–vegetation relationships. Baseline temperature and moisture availability strongly shaped climate effects on canopy traits and productivity, whereas canopy‐property–productivity relationships varied little across space. Positive productivity responses to warming were stronger in wetter and more seasonally variable climatic contexts, but weakened where baseline winter snow accumulation was greater. Together, our findings show that short‐term productivity responses in mountain grasslands reflect a balance between direct energetic constraints and indirect pathways through integrated canopy functional properties, and that this balance varies along macroclimatic gradients.
