Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from -9 to +26 °C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained <0.5% of the variation for Green tea and 5% for Rooibos tea, and was of significance only under unfavorable decomposition conditions (i.e. xeric versus mesic environments). When the data were aggregated at the biome scale, climate played a significant role on decomposition of both litter types (explaining 64% of the variation for Green tea and 72% for Rooibos tea). No significant effect of land-use on early stage litter decomposition was noted within the temperate biome. Our results indicate that multiple drivers are affecting early stage litter mass loss with litter quality being dominant. In order to be able to quantify the relative importance of the different drivers over time, long-term studies combined with experimental trials are needed.

In most woody plants, leaf morphological and physiological characteristics are extremely variable across environmental gradients, particularly across altitudinal gradients. Hippophae rhamnoides L., a dioecious and deciduous shrub species, occupies a wide range of habitats in the Wolong Nature Reserve, southwest China. We measured growth, sex ratio and morphological and physiological characteristics of leaves in male and female H. rhamnoides individuals along an altitudinal gradient. Shoot height (HT), leaf N concentration per unit dry mass (N(mass)), leaf N concentration per unit area (N(area)) and leaf carbon isotope composition (delta(13)C) were higher in males than in females, whereas females had higher specific leaf area (SLA), stomatal length (SL) and stomatal index (SI) (i.e., total stomatal length per unit leaf area) than males along the altitudinal gradient. Females also had higher values of stomatal density (SD) at all altitudes except 2800 m. The male:female ratio (MFR) was biased toward males at all altitudes except at 2800 m. Changes in HT, MFR, SLA, SD, SL, SI, N(mass), N(area) and delta(13)C along the altitudinal gradient were nonlinear. Below 2800 m, HT, SLA, SD, SL and SI increased with increasing altitude, but above 2800 m they decreased with increasing altitude. In contrast, MFR, N(mass), N(area) and delta(13)C showed the opposite patterns with altitude. Consequently, we confirmed our hypotheses: (1) stressful environments have a more negative impact on females than on males in a variety of ways; (2) under optimal growth conditions the sex ratio is even, but becomes male-biased as resources become limited; and (3) there is an optimum altitudinal range at around 2800 m for the growth of H. rhamnoides in the Wolong Nature Reserve.

[1] We studied the interannual variability of cumulative net ecosystem CO 2 exchange (NEE) and its connection with cumulative or average climatic variables during five growing seasons. The analysis was based on a 5-year-long time series of CO 2 flux measured from April 1996 to April 2001 in a Scots pine forest in southern Finland by the eddy covariance technique. The onset of the ecosystem growing season was best connected with air temperature, and the end of the growing season was best connected with day length. With these variables we were able to predict the timing and the length of each growing season within 0-3 days. The forest was a sink of carbon with little interannual variability: The uptake during the four full growing seasons varied by 80 g C m À2 , ranging from 230 to 310 g C m À2 . The estimated winter release each year varied between 60 and 90 g C m À2 . The interannual variation in seasonal (spring, summer, autumn) carbon exchange ranged from 30 g C m À2 in autumn and spring to 80 g C m À2 in summer. The average climatic variables explained the variability of the seasonal or growing-season cumulative NEE only partly. Both the daytime and the nighttime CO 2 fluxes contributed markedly to the variability in carbon exchange, indicating that photosynthesis and respiration have an equally important influence on NEE.

Frost events during the active growth period of plants can cause extensive frost damage with tremendous economic losses and dramatic ecological consequences. A common assumption is that climate warming may bring along a reduction in the frequency and severity of frost damage to vegetation. On the other hand, it has been argued that rising temperature in late winter and early spring might trigger the so called “false spring”, that is, early onset of growth that is followed by cold spells, resulting in increased frost damage. By combining daily gridded climate data and 1,489 k in situ phenological observations of 27 tree species from 5,565 phenological observation sites in Europe, we show here that temporal changes in the risk of spring frost damage with recent warming vary largely depending on the species and geographical locations. Species whose phenology was especially sensitive to climate warming tended to have increased risk of frost damage. Geographically, compared with continental areas, maritime and coastal areas in Europe were more exposed to increasing occurrence of frost and these late spring frosts were getting more severe in the maritime and coastal areas. Our results suggest that even though temperatures will be elevated in the future, some phenologically responsive species and many populations of a given species will paradoxically experience more frost damage in the future warming climate. More attention should be paid to the increased frost damage in responsive species and populations in maritime areas when developing strategies to mitigate the potential negative impacts of climate change on ecosystems in the near future.

We exposed seedlings of 12 Eucalyptus microtheca F. Muell. provenances to well-watered and waterstressed growing conditions in a greenhouse experiment and investigated the effects of drought on various plant properties in the provenances. We found significant variation in total biomass, height, root mass/foliage area ratio, foliage area/stem cross sectional area ratio, specific leaf area (SLA), water-use efficiency (WUE) and carbon isotope composition (δ 13 C) among the provenances. The observed inter-provenance variation was more pronounced in the water-stressed treatment than in the well-watered one. Drought increased root mass/foliage area ratio, foliage area/stem cross sectional area ratio, WUE, δ 13 C and decreased total biomass, height, transpiration and SLA. We also analysed relationships between plant properties and climate of native habitats of the provenances and found that most properties were strongly correlated with mean driest quarter rainfall. The correlation was positive for total biomass, height, transpiration and SLA and negative for root mass/foliage area ratio, foliage area/stem cross sectional area ratio, WUE and δ 13 C. Finally, we evaluated the intra-specific variation in foliage area/stem cross sectional area ratio in the context of tree hydraulic architecture: provenances from dry areas and trees grown under drought stress had more foliage per stem area ratio. However, their transpiration and the length of their hydraulic pathway were smaller and therefore the root to leaf water potential gradient might be smaller in these trees.

Coniferous trees growing in the boreal and temperate zones have a clear annual cycle of photosynthetic activity. A recent study demonstrated that the seasonal variation in photosynthetic capacity of Scots pine (Pinus sylvestris L.) could be attributed mainly to the light response curve of photosynthesis. The magnitude of the light response curve varied over the season while its shape remained constant, indicating that the two physiological parameters quantifying the curve-the quantum yield per unit internal carbon dioxide concentration and the corresponding light-saturated rate-remained proportional to each other. We now show, through modeling studies, that the quantum yield (and hence the light-saturated rate) is related to the annual cycle of temperature through a delayed dynamic response. The proposed model was tested by comparing model results with intensive measurements of photosynthesis and driving variables made from April to October in three shoots of Scots pine growing near the northern timberline. Photosynthetic capacity showed considerable acclimation during the growing season. A single model describing photosynthetic capacity as a reversible, first-order delay process driven by temperature explained most of the variation in photosynthetic capacity during the year. The proposed model is simpler but no less accurate than previous models of the annual cycle of photosynthetic capacity.

Disentangling ecological processes that influence community assembly and species diversity across spatial scales remains a major goal of community ecology. Community assembly processes influence spatial patterns of species diversity through their interactions with key functional traits. Hence, quantifying spatial patterns of functional trait diversity (FD) represents a useful tool for disentangling the relative importance of abiotic filtering, biotic interactions, random assembly and dispersal limitation across spatial scales. Here, we measured 12 traits of 112 study species in a 20‐ha fully mapped subtropical forest plot. The individuals of the 112 study species account for 99% of all living stems with diameter at breast height ≥ 1 cm. We studied important functional traits related to physiological processes of plants including resource acquisition (e.g. CO2 assimilation rate and leaf nutrient concentration) and drought tolerance (e.g. stem hydraulic conductivity and leaf turgor loss point). Additionally, species abundance, spatial locations (x‐ and y‐coordinates for each individual of the 112 study species) as well as topographic and soil variables that represent potentially important attributes of the physical environment of the plot were also included in our dataset. We employed two FD‐based tests (comparing FD within communities to those from random communities, distance‐based Moran's eigenvector maps (MEM) and redundancy analysis‐based variance partitioning), and one spatial analysis (inhomogeneous bivariate pair correlation analysis) to quantify the spatial patterns of FD of the plot at multiple spatial scales (400, 900, 1,600, 2,500 and 10,000 m2). We demonstrate that abiotic filtering is the major determinant responsible for trait convergence at relatively small scales (400, 900 and 1,600 m2), whereas dispersal limitation becomes dominant, causing the weakening of trait convergence at relatively large scales (2,500 and 10,000 m2). Our results highlight the relative contributions of different ecological processes to community assembly at different spatial scales, which can be distinguished using the diversity patterns of key functional traits. Also, our integrated approaches constitute a useful study design to disentangle variable ecological processes in shaping community assembly across spatial scales. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13079/suppinfo is available for this article.

Forest fires are one of the most important natural disturbances in boreal forests, and their occurrence and severity are expected to increase as a result of climate warming. A combination of factors induced by fire leads to a thawing of the near-surface permafrost layer in subarctic boreal forest. Earlier studies reported that an increase in the active layer thickness results in higher carbon dioxide (CO) and methane (CH) emissions. We studied changes in CO, CH and nitrous oxide (NO) fluxes in this study, and the significance of several environmental factors that influence the greenhouse gas (GHG) fluxes at three forest sites that last had fires in 2012, 1990 and 1969, and we compared these to a control area that had no fire for at least 100years. The soils in our study acted as sources of CO and NO and sinks for CH. The elapsed time since the last forest fire was the only factor that significantly influenced all studied GHG fluxes. Soil temperature affected the uptake of CH, and the NO fluxes were significantly influenced by nitrogen and carbon content of the soil, and by the active layer depth. Results of our study confirm that the impacts of a forest fire on GHGs last for a rather long period of time in boreal forests, and are influenced by the fire induced changes in the ecosystem.