Montiel-González Cristina, Tapia-Torres Yunuen, Souza Valeria, García-Oliva Felipe
Instituto de Investigaciones en Ecosistemas y Sustentabilidad, Universidad Nacional Autónoma de México, Morelia, Michoacán, Mexico.
Escuela Nacional de Estudios Superiores Unidad Morelia, Universidad Nacional Autónoma de México, Morelia, Michoacán, Mexico.
PeerJ. 2017 Nov 9;5:e4007. doi: 10.7717/peerj.4007. eCollection 2017.
Soil microbial communities (SMC) play a central role in the structure and function of desert ecosystems. However, the high variability of annual precipitation could results in the alteration of SMC and related biological processes depending on soil water potential. The nature of the physiological adjustments made by SMC in order to obtain energy and nutrients remains unclear under different soil resource availabilities in desert ecosystems. In order to examine this dynamic, the present study examined the effects of variation in annual precipitation on physiological adjustments by the SMC across two vegetation-soil systems of different soil organic matter input in an oligotrophic desert ecosystem.
We collected soil samples in the Cuatro Ciénegas Basin (Mexico) under two vegetation covers: rosetophylous scrub (RS) and grassland (G), that differ in terms of quantity and quality of organic matter. Collections were conducted during the years 2011, 2012, 2013 and 2014, over which a noticeable variation in the annual precipitation occurred. The ecoenzymatic activity involved in the decomposition of organic matter, and the concentration of dissolved, available and microbial biomass nutrients, were determined and compared between sites and years.
In 2011, we observed differences in bacterial taxonomic composition between the two vegetation covers. The lowest values of dissolved, available and microbial nutrients in both cover types were found in 2012. The G soil showed higher values of dissolved and available nutrients in the wet years. Significant positive correlations were detected between precipitation and the ratios Cmic:Nmic and Cmic:Pmic in the RS soil and Cmic:Pmic and Nmic:Pmic in the G soil. The slopes of the regression with Cmic and Nmic were higher in the G soil and lower in the RS soil. Moreover, the SMC under each vegetation cover were co-limited by different nutrients and responded to the sum of water stress and nutrient limitation.
Soil community within both sites (RS and G) may be vulnerable to drought. However, the community of the site with lower resources (RS) is well adapted to acquire P resources by ecoenzyme upregulation during years with adequate precipitation, suggesting that this community is resilient after drought occurs. Under the Global Climate Change scenarios for desert ecosystems that predict reduced annual precipitation and an increased intensity and frequency of torrential rains and drought events, the soil microbial communities of both sites could be vulnerable to drought through C and P co-limitation and reallocation of resources to physiological acclimatization strategies in order to survive.
土壤微生物群落（SMC）在沙漠生态系统的结构和功能中起着核心作用。然而，年降水量的高度变异性可能导致SMC及相关生物过程根据土壤水势发生改变。在沙漠生态系统中，不同土壤资源可利用性条件下，SMC为获取能量和养分所进行的生理调节的本质仍不清楚。为了研究这种动态变化，本研究考察了年降水量变化对贫营养沙漠生态系统中两个不同土壤有机质输入的植被 - 土壤系统中SMC生理调节的影响。
我们在墨西哥的夸特罗谢内加斯盆地采集了两种植被覆盖下的土壤样本：莲座叶灌丛（RS）和草地（G），它们在有机质的数量和质量上存在差异。采集工作在2011年、2012年、2013年和2014年进行，这期间年降水量有显著变化。测定并比较了不同地点和年份之间参与有机质分解的生态酶活性以及溶解态、有效态和微生物生物量养分的浓度。
2011年，我们观察到两种植被覆盖下细菌分类组成存在差异。两种覆盖类型中溶解态、有效态和微生物养分的最低值出现在2012年。在湿润年份，G土壤的溶解态和有效态养分含量较高。在RS土壤中，降水量与Cmic:Nmic和Cmic:Pmic比值之间以及在G土壤中降水量与Cmic:Pmic和Nmic:Pmic比值之间均检测到显著正相关。G土壤中Cmic和Nmic回归斜率较高，RS土壤中较低。此外，每种植被覆盖下的SMC受到不同养分的共同限制，并对水分胁迫和养分限制的总和做出响应。
两个地点（RS和G）的土壤群落可能都易受干旱影响。然而，资源较少地点（RS）的群落能够很好地适应在降水充足的年份通过上调生态酶来获取P资源，这表明该群落在干旱发生后具有恢复力。在预测年降水量减少以及暴雨和干旱事件强度和频率增加的沙漠生态系统全球气候变化情景下，两个地点的土壤微生物群落可能会因C和P的共同限制以及为了生存而将资源重新分配到生理适应策略而易受干旱影响。
