Contributions of Soil Communities to Ecosystem Respiration and Greenhouse Gas Emmisions in a Piñon-Juniper Woodland at the Sevilleta National Widlife Refuge, New Mexico (2011)

Global climate change processes, especially prolonged droughts and increasingly high temperatures, are significantly affecting numerous arid ecosystems across the state of New Mexico.  One of the more adversely affected ecosystems in New Mexico is piñon-juniper woodland (PJ), which includes areas near Mountainair, New Mexico, USA.  Because changes in ambient temperature and decreases in water availability show pervasive effects on the above-ground status of existing PJ woodlands in New Mexico, it seems likely that the effects of changes in these two master variables will manifest themselves within soil processes such as soil organic matter (SOM) decomposition rates and soil respiration rates, as well as nutrient cycling rates and availabilities to both plants and soil microbial communities. We conducted analyses of soil physicochemical properties and soil fungal biomass via soil ergosterol content, as well as evaluating the activity rates of multiple hydrolytic exoenzymes, which are indicative of fungal activity in soils.  Samples were collected from multiple tree-to-tree competition gradients that were identified in May/June of 2011.  These gradients were established based on the type of mycorrhizal fungus types expected to occupy the soil community established beneath the canopy of a focal tree, with there being two focal trees in each gradient.  Gradients were established between two live piñon trees (Pinus edulis), two juniper trees (Juniperus monosperma), a live piñon and live juniper, and a dead piñon and live juniper.  We only sampled from under live trees at the control site.In order to obtain these samples, we collected soil samples from two different sites in a PJ woodland located within the boundaries of the Deer Canyon ranch. Changes in soil conditions were captured by sampling from the two sites at multiple times throughout the summer of 2011.  We collected samples from Dr. Marcy Litvak’s girdled PJ woodland eddy-flux tower site in June, July, August and finally in late September.  We also collected samples from Dr. Litvak’s control PJ woodland tower site in June and September of 2011.  Significant differences in the activity rates of the hydrolytic exoenzymes alanine aminopeptidase, alkaline phosphatase, β-d-glucosidase, and β-N-acetyl glucosaminidase were observed within soils collected at multiple times from June through September when comparing the observed rates of activities under the trees in the live piñon to live piñon gradients vs. the juniper to juniper gradients.  These differences were observed in samples from multiple dates at the girdled site without there being significant differences in soil fungal biomass across seasons or study sites.  Continued work with the established sites on a year-to-year basis could provide an insight into how the fungal communities within New Mexican PJ woodlands will respond to future changes in soil conditions as global climate change processes advance in New Mexico.

全球气候变化过程，尤其是长期干旱与持续攀升的气温，正显著影响美国新墨西哥州境内的众多干旱生态系统。
新墨西哥州受负面影响较显著的生态系统之一为矮松-杜松林地（piñon-juniper woodland, PJ），其分布范围涵盖美国新墨西哥州芒蒂尔附近区域。鉴于环境温度变化与水资源可利用性下降，已对新墨西哥州现存PJ林地的地上部分造成广泛影响，因此这两项关键变量的变化，大概率会体现在土壤过程中——包括土壤有机质（soil organic matter, SOM）分解速率、土壤呼吸速率，以及养分循环速率与植物、土壤微生物群落可获取的养分水平。
本研究通过测定土壤麦角固醇含量，分析了土壤理化性质与土壤真菌生物量，同时评估了多种水解胞外酶的活性速率，这类酶可作为土壤中真菌活性的指示物。样本采集自2011年5-6月间确定的多组树间竞争梯度。每个梯度设置2株目标树，梯度划分依据为预期占据目标树冠下土壤群落的菌根真菌类型。梯度类型涵盖：两株活矮松（Pinus edulis）、两株活杜松（Juniperus monosperma）、一株活矮松与一株活杜松，以及一株枯矮松与一株活杜松。本研究仅在对照样地的活树下方开展采样。
为获取上述样本，我们在鹿溪牧场（Deer Canyon ranch）辖内的PJ林地内的两处不同样地采集土壤样本。通过在2011年夏季的多个时间点对两处样地进行采样，以捕捉土壤条件的动态变化。我们分别于2011年6月、7月、8月及9月下旬，在马西·利特瓦克（Marcy Litvak）博士的环剥PJ林地涡度通量塔样地采集样本；同时于2011年6月与9月，在利特瓦克博士的对照PJ林地涡度通量塔样地开展采样。
对比活矮松-活矮松梯度与杜松-杜松梯度下树木下方的土壤样本，在6月至9月的多个采样时间点中，观测到水解胞外酶——丙氨酸氨基肽酶、碱性磷酸酶、β-D-葡萄糖苷酶与β-N-乙酰氨基葡萄糖苷酶——的活性速率存在显著差异。上述差异在环剥样地的多批次采样中均有体现，但不同季节与研究样地间的土壤真菌生物量并无显著差异。
未来可基于本研究建立的样地开展年度追踪研究，以揭示新墨西哥州PJ林地内的真菌群落，将如何随着全球气候变化进程下新墨西哥州土壤条件的持续改变而产生响应。