Xujun Ma

Biomass allocation is crucial for predicting ecosystem responses to global change, and yet, whether patterns follow the plastic optimal partitioning theory (OPT) or the constrained allometric partitioning theory (APT) remains contentious across different biomes. A key uncertainty is whether vast, functionally distinct ecosystems, such as temperate and alpine drylands, show different allocation strategies. Here, we investigated root:shoot ratio (R/S) patterns across 120 sites spanning temperate and alpine drylands in northern China. Significant differences in allocation were observed, with temperate drylands showing lower R/S than alpine regions. In temperate drylands, R/S scaled allometrically with plant community size, consistent with APT, with key soil factors exerting only an indirect influence through their effects on plant community size. Conversely, in alpine drylands, R/S was insensitive to plant community size and instead responded directly to the mean annual temperature, a pattern indicative of OPT. We propose that this strategic divergence is linked to their underlying community functional structures. Communities with greater functional dissimilarity may achieve higher niche complementarity, providing the necessary capacity to optimize allocation in response to environmental constraints. Our findings demonstrate that climatic regimes drive alternative biomass allocation strategies, providing both a predictive framework for vegetation responses and a theoretical basis for dryland ecosystem restoration under climate change.

Using a Non-invasive Micro-test Technique, flux profiles of Cd²⁺, Ca²⁺, and H⁺ were investigated in axenically grown cultures of two strains of Paxillus involutus (MAJ and NAU), ectomycorrhizae formed by these fungi with the woody Cd²⁺-hyperaccumulator, Populus × canescens, and non-mycorrhizal (NM) roots. The influx of Cd²⁺ increased in fungal mycelia, NM and ectomycorrhizal (EM) roots upon a 40-min shock, after short-term (ST, 24 h), or long-term (LT, 7 days) exposure to a hydroponic environment of 50 μM CdCl₂. Cd²⁺ treatments (shock, ST, and LT) decreased Ca²⁺ influx in NM and EM roots but led to an enhanced influx of Ca²⁺ in axenically grown EM cultures of the two P. involutus isolates. The susceptibility of Cd²⁺ flux to typical Ca²⁺ channel blockers (LaCl₃, GdCl₃, verapamil, and TEA) in fungal mycelia and poplar roots indicated that the Cd²⁺ entry occurred mainly through Ca²⁺-permeable channels in the plasma membrane (PM). Cd²⁺ treatment resulted in H₂O₂ production. H₂O₂ exposure accelerated the entry of Cd²⁺ and Ca²⁺ in NM and EM roots. Cd²⁺ further stimulated H⁺ pumping activity benefiting NM and EM roots to maintain an acidic environment, which favored the entry of Cd²⁺ across the PM. A scavenger of reactive oxygen species, DMTU, and an inhibitor of PM H⁺-ATPase, orthovanadate, decreased Ca²⁺ and Cd²⁺ influx in NM and EM roots, suggesting that the entry of Cd²⁺ through Ca²⁺-permeable channels is stimulated by H₂O₂ and H⁺ pumps. Compared to NM roots, EM roots exhibited higher Cd²⁺-fluxes under shock, ST, and LT Cd²⁺ treatments. We conclude that ectomycorrhizal P. × canescens roots retained a pronounced H₂O₂ production and a high H⁺-pumping activity, which activated PM Ca²⁺ channels and thus facilitated a high influx of Cd²⁺ under Cd²⁺ stress.