Root exudation is a key plant function with a large influence on soil organic matter dynamics and plant–soil feedbacks in forest ecosystems. Yet despite its importance, the main ecological drivers of ...root exudation in mature forest trees remain to be identified.
During two growing seasons, we analyzed the dependence of in situ collected root exudates on root morphology, soil chemistry and nutrient availability in six mature European beech (Fagus sylvatica L.) forests on a broad range of bedrock types.
Root morphology was a major driver of root exudation across the nutrient availability gradient. A doubling of specific root length exponentially increased exudation rates of mature trees by c. 5-fold. Root exudation was also closely negatively related to soil pH and nitrogen (N) availability. At acidic and N-poor sites, where fungal biomass was reduced, exudation rates were c. 3-fold higher than at N- and base-richer sites and correlated negatively with the activity of enzymes degrading less bioavailable carbon (C) and N in the bulk soil.
We conclude that root exudation increases on highly acidic, N-poor soils, in which fungal activity is reduced and a greater portion of the assimilated plant C is shifted to the external ecosystem C cycle.
Forest trees facing climate change may persist in a short term through acclimation within the limits of their phenotypic plasticity. In the longer term, however, evolutionary adaptation would be ...needed for populations to thrive in the changed climate, or species may migrate to new areas as climate becomes favorable there. European beech is one of the most important tree species in western and central Europe, and projections indicate that it may contract its southern range and migrate towards northern and north-eastern Europe in the future climates. It is therefore important to recognize the level of variation in climatic adaptation and climatic responsiveness of populations which are likely the source of genetic material for expanding the species range. In this study we examined variation in growth and productivity among 39 European beech populations, which represent the north-eastern margin of the species distribution range. We employed the transfer function and the Universal Response Function approaches to analyze populations’ performance in response to the climatic transfer across five provenance test sites and in relationship to climate at the populations’ origin and planting sites. We found significant but low variation among tested populations in tree diameter (DBH; cm) and Volume index (m3 ha−1) and significant population × site interaction at age 30 years. That variation, however, was only weakly related to gradients of climatic variables represented by the set of sampled populations. The variable performance of populations across planting sites, and the importance of planting sites’ climate in explaining traits’ variation in this experiment confirm the plastic response of examined populations to climate change. Our findings indicate that beech populations from the analyzed region have a high acclimation potential to the projected changes in climate, although for high-altitude populations (from > 600 m a.s.l) the negative effect of transfers to warmer and drier conditions was observed. Detailed knowledge of the plasticity of response and adaptive potential of marginal beech populations in the longer term would be needed to guide management decisions to help future forests to cope with climate change.
•Beech populations at species north-east margin would contribute to range expansion.•Those populations vary in diameter growth and productivity across planting sites.•Variation was related more to the climate of planting site than population origin.•The pattern on variation reflects plastic response to climate change.•Beech populations from analyzed region have overall a high acclimation potential.
Forest management aims for productive and stable forests that continuously provide ecosystem goods and services, including balancing nutrient fluxes. Increasing heat and frequent droughts in ...temperate European forests make the introduction of non-native Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) an increasingly relevant climate change adaptation strategy, particularly as an admixture to native tree species, such as European beech (Fagus sylvatica L.). Douglas fir can alter biogeochemical processes in forest soils, potentially leading to an excess of nitrogen in the ecosystem, but the biotic and abiotic controls of this effect need further examination (species interactions, soil type). Here we studied nitrate leaching on plots of two contrasting textures (southern loamy and northern sandy site) planted with either pure Douglas fir, pure Norway spruce (Picea abies L. Karst.), pure European beech or a mixture of beech with either of the conifers. We used P80 suction lysimeters at 5 and 60 cm soil depth and collected soil solution over two continuous years to estimate nitrate leaching risks. We found highest concentrations of nitrate in soil solution in lower soil layers under Douglas fir (29.14 mg/L), which corroborates the findings of some studies conducted in pure stands. Comparisons of concentrations below the litter layer and below the main rooting zone implied that accumulation and microbial production of nitrate is taking place under Douglas fir. In Douglas fir-beech mixed stands, however, we found sustained significantly lower nitrate concentrations in soil solution below the main rooting zone (1.68 mg/L), implying a mixture effect. Furthermore, site played a key role in controlling nitrate concentrations in soil solution under Douglas fir on sites with finer soil texture and a lower C:N ratio. Elevated nitrate concentrations were associated with a P-limitation found in the trees, which likely caused reduced nitrate uptake. We discuss the results with regards to throughfall, litter, soil and microbial characteristics. We conclude that increased nitrate concentrations under Douglas fir stands may pose a relatively higher nitrate leaching risk than Norway spruce and a considerably higher risk compared to beech stands. However, the low susceptibility to leaching under beech stands seems to be a strong effect trait in mixtures, diminishing the high leaching potential Douglas fir induces on some sites. Low leaching potential is key to sustaining adequate nutrition in temperate forests and reducing pollution of groundwater. Our findings strongly urge forestry experts to carefully assess site conditions and foster mixtures with European beech when planting Douglas fir.
•Tree species affect nitrogen cycling; Douglas fir can increase nitrate concentrations in soil solution, posing a risk for nitrate leaching.•When mixed with European beech, nitrate concentrations remain low.•On sandy, poorer sites, nitrate leaching was much lower than on loamy sites.•P-limitation of Douglas fir caused reduced N uptake, leading to N accumulation in soil solution.•Nitrate production by microorganisms was likely stimulated under Douglas fir.
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