Thresholds in decoupled soil-plant elements under changing climatic conditions
Background and aims
Aridity has increased in the past decades and will probably continue to increase in arid and semiarid regions. Here we decipher the plant and soil capacity to retain metal cations when climate evolves to more arid conditions.
We analyzed K, Na, Ca, Mg, Fe, Mn, Zn and Cu concentrations in 580 soil samples and 666 plant (shoot and root) samples along a 3600 km aridity gradient in northern China.
The concentrations of soil exchangeable K, Mg, Mn, Fe and Cu clearly decreased with increasing aridity due to the relationships of aridity with soil clay content and soil pH. Increases in exchangeable Na and Ca concentrations at mid- and high-aridity levels are probably due to the soil salinization, whereas increased exchangeable Fe concentrations at extreme levels of aridity may be more related to a reduced pH. Element concentrations in both plant shoots and roots were unrelated to soil exchangeable element concentrations; instead they increased monotonously with increasing aridity, corresponding with decreases in plant size and shoot/root ratios. The shoot/root mineralomass ratios in general increased with increasing aridity. The proportional higher element contents in shoots than in roots with increasing aridity are related to increased water uptake and/or use efficiency.
The extractability of soil elements in response to changing climate varied with the nature of specific elements that are controlled by biological and geochemical processes, i.e., some decreased linearly with increasing aridity, whereas others first decreased and then increased with different thresholds. These contrasting effects of aridity on nutrient availability could further constrain plant growth and should be incorporated into biogeochemical models. The prevailing paradigm of a positive relationship between concentrations of plant and soil elements needs to be reconsidered under changing climatic conditions.
KeywordsAridity Biogeochemical cycles Clay Climate change Soil pH Threshold
We thank all members of the Field Expedition Team from the Institute of Applied Ecology, Chinese Academy of Sciences for assistance with field data collection. We also thank the Erguna Forest-Steppe Ecotone Research Station, Institute of Applied Ecology, Chinese Academy of Sciences. This work was financially supported by the National Natural Science Foundation of China (41371251), by the National Basic Research Program of China (2011CB403204), and State Key Laboratory of Forest and Soil Ecology (LFSE2013-01). JP and JS acknowledge funding from the European Research Council Synergy grant ERC-2013-SyG-610028 IMBALANCE-P, the Spanish Government grant CGL2013-48074-P and the Catalan Government grant SGR 2014-274.
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