Soil Science, TUM School of Life Sciences, Technical University of Munich, Freising-Weihenstephan, Germany.
Land Surface Atmosphere Interactions - AG Ecophysiology of Plants, TUM School of Life Sciences, Technical University of Munich, Freising-Weihenstephan, Germany.
Glob Chang Biol. 2024 Oct;30(10):e17519. doi: 10.1111/gcb.17519.
In drylands, where water scarcity limits vascular plant growth, much of the primary production occurs at the soil surface. This is where complex macro- and microbial communities, in an intricate bond with soil particles, form biological soil crusts (biocrusts). Despite their critical role in regulating C and N cycling in dryland ecosystems, there is limited understanding of the fate of biologically fixed C and N from biocrusts into the mineral soil, or how climate change will affect C and N fluxes between the atmosphere, biocrusts, and subsurface soils. To address these gaps, we subjected biocrust-soil systems to experimental warming and drought under controlled laboratory conditions, monitored CO fluxes, and applied dual isotopic labeling pulses (CO and N). This allowed detailed quantification of elemental pathways into specific organic matter (OM) pools and microbial biomass via density fractionation and phospholipid fatty acid analyses. While biocrusts modulated CO fluxes regardless of the temperature regime, drought severely limited their photosynthetic C uptake to the extent that the systems no longer sustained net C uptake. Furthermore, the effect of biocrusts extended into the underlying 1 cm of mineral soil, where C and N accumulated as mineral-associated OM (MAOM). This was strongly associated with increased relative dominance of fungi, suggesting that fungal hyphae facilitate the downward C and N translocation and subsequent MAOM formation. Most strikingly, however, these pathways were disrupted in systems exposed to warming, where no effects of biocrusts on the elemental composition of the underlying soil nor on MAOM were determined. This was further associated with reduced net biological N fixation under combined warming and drought, highlighting how changing climatic conditions diminish some of the most fundamental ecosystem functions of biocrusts, with detrimental repercussions for C and N cycling and the persistence of soil organic matter pools in dryland ecosystems.
在干旱地区，由于水资源短缺限制了维管束植物的生长，大部分初级生产力都发生在土壤表面。正是在这个地方，复杂的宏观和微生物群落与土壤颗粒形成了生物土壤结皮（biocrusts）。尽管它们在调节干旱生态系统中的碳氮循环方面起着至关重要的作用，但对于生物固定的碳和氮从生物结皮进入矿物土壤的去向，以及气候变化将如何影响大气、生物结皮和地下土壤之间的碳氮通量，我们的了解还很有限。为了填补这些空白，我们在受控的实验室条件下对生物结皮-土壤系统进行了实验性的增温和干旱处理，监测了 CO 通量，并应用了双重同位素标记脉冲（CO 和 N）。这使得我们能够通过密度分级和磷脂脂肪酸分析详细量化进入特定有机物质（OM）库和微生物生物量的元素途径。尽管生物结皮无论在何种温度条件下都能调节 CO 通量，但干旱严重限制了它们的光合作用碳吸收，以至于系统不再维持净碳吸收。此外，生物结皮的影响延伸到下面 1 厘米的矿物土壤中，其中 C 和 N 作为与矿物结合的有机物质（MAOM）积累。这与真菌相对优势的增加密切相关，表明真菌菌丝促进了向下的碳和氮转移以及随后的 MAOM 形成。然而，最引人注目的是，这些途径在暴露于增温的系统中被打乱，生物结皮对下面土壤的元素组成或 MAOM 没有任何影响。这进一步与在增温和干旱的共同作用下净生物固氮减少有关，突出了气候变化条件如何削弱了生物结皮的一些最基本的生态系统功能，对碳氮循环以及干旱生态系统中土壤有机质库的持久性产生了不利影响。
