Fungal connections between plants and biocrusts

Treatments_180914 file:<br>2x2 experimental design with mesocosms with field-collected Bouteloua gracilis and associated rhizosphere soil and biocrusts. <br><br>Fungal connection treatment: For the intact fungal connections treatment, we used mesh with 50μm pores (Small Parts, Fort Meade, FL) to inhibit fine roots but allow fungal hyphae to pass through. For the impeded treatment, we used mesh with 0.45μm pores (GE Healthcare Life Science, Pittsburg, PA) to inhibit both roots and fungi. The mesh was placed horizontally under the biocrust (~0.5 – 1cm depth) with a small hole (~5 cm diameter) in the center to allow bunchgrass shoots to pass through. <br><br><br> Precipitation regime: We applied small,<b> </b>frequent events (100mL/pot once per week, a 2.5mm event) or large,<b> </b>infrequent<b> </b>events<b> </b>(400mL/pot once per month, a 10mm event) during August through October in 2013 and May through October in 2014 and 2015. <br><br>Response variables for each pot:- CN_r_ecol_180914 file: Percentage C and N by mass for crust and leaf from elemental analyzer.<br>- EEA_ecol_180914 file: Extracellular enzyme activity (nmol h^-1 g^-1) and organic matter percentage (Loss on ignition). β-1,4-glucosidase (BG), β-1,4- <i>N </i>-acetylglucosaminidase (NAG), and leucine aminopeptidase (LAP)<br>-PChSc_r_ecol_180914 file: Chlorophyll content for biocrust samples ("CHAugperg") and plant root crown dimensions ("shoot_largest_diameter_cm" and "shoot_perpendicular_diameter_cm") for each sampling period 2013-2015.<br>root_ecol_180914 file: Roots in 1.9cm diameter x 5cm deep soil core (g_root_intop5cm), in 19.cm diameter x .5cm deep crust sample, colonization of septate and aseptate hyphae in roots, and ergosterol content (ug g^-1) in bulk soil and crust.<br><br> seeds_ecol_180914 file: total mass of seed heads (g) at end of growing season (Oct) of 2014 and 2015. <br><br><br><br> 15N tracer experiment: To investigate N transfer from biocrust to plants, we added a total of 800μL of 0.86M ¹⁵N-NaNO₃ (8 mg N) to two points of biocrust on opposite sides of the plant (~6cm from root crown) during October 2015. <br><br>mass_balance_180914 file: sample type (crust, root, or leaf), time (h) since 15N tracer added (0=before label added), whether the pot had tracer added ("labeled15N"), the delta 15N value, the average mass percentage N, and the destructive harvest shoot and root values.<br><br>

Treatments_180914 文件：本实验采用2×2因子设计，以野外采集的格兰马草（Bouteloua gracilis）及其根际土壤与生物结皮（biocrusts）构建中型生态箱（mesocosms）。

真菌连接处理：对于完整真菌连接组，我们使用孔径50μm的网筛（Small Parts，佛罗里达州米德堡），以阻隔细根但允许真菌菌丝穿透；对于阻隔组，我们使用孔径0.45μm的网筛（GE Healthcare Life Science，宾夕法尼亚州匹兹堡），同时抑制根系与真菌生长。网筛水平放置于生物结皮下约0.5–1cm深度处，中心开设直径约5cm的小孔，以供丛生禾草的茎秆穿出。

降水处理模式：2013年8月至10月、2014年与2015年5月至10月期间，我们设置两种降水处理：其一为小型高频降水（每盆每周施加100mL，对应降水深度2.5mm），其二为大型低频降水（每盆每月施加400mL，对应降水深度10mm）。

各盆栽的响应变量如下：
- CN_r_ecol_180914 文件：通过元素分析仪测定的结皮与叶片的碳、氮质量百分比。
- EEA_ecol_180914 文件：胞外酶活性（extracellular enzyme activity，单位：nmol h^-1 g^-1）与有机质百分比（灼烧减重法（Loss on ignition）测定），涵盖β-1,4-葡萄糖苷酶（β-1,4-glucosidase，BG）、β-1,4-N-乙酰葡糖胺糖苷酶（β-1,4-N-acetylglucosaminidase，NAG）以及亮氨酸氨肽酶（leucine aminopeptidase，LAP）。
- PChSc_r_ecol_180914 文件：2013–2015年各采样周期内，生物结皮样品的叶绿素含量（标注为“CHAugperg”），以及植物根冠尺寸指标（“shoot_largest_diameter_cm”与“shoot_perpendicular_diameter_cm”）。
- root_ecol_180914 文件：1.9cm直径×5cm深土芯中的根系生物量（g_root_intop5cm）、19cm直径×0.5cm深结皮样品中的根系含量，根系内分隔菌丝与无隔菌丝的定殖情况，以及块状土壤与结皮中的麦角固醇（ergosterol）含量（单位：μg g^-1）。
- seeds_ecol_180914 文件：记录2014年与2015年生长季末期（10月）的穗状花序总干重（单位：g）。

¹⁵N示踪实验：为探究生物结皮向植物的氮素转移过程，我们于2015年10月在植株两侧（距根冠约6cm）的两处生物结皮点位，共施加800μL浓度为0.86M的¹⁵N-硝酸钠（含8mg氮）。

mass_balance_180914 文件：包含样品类型（结皮、根系或叶片）、施加¹⁵N示踪剂后的采样时长（小时，0代表标记施加前）、盆栽是否施加示踪剂（"labeled15N"）、δ¹⁵N值、平均氮质量百分比，以及破坏性收获获得的地上部与地下部生物量数据。