Understanding environmental factors controlling vegetation and soil attributes is crucial for the prediction of future climate change impacts on ecosystem functioning. This study conducted at 10 sites in South Mediterranean grasslands along aridity gradient aims to determine the possible controlling factors (mean annual precipitation MAP, mean annual temperature MAT and soil pH) that may affect vegetation attributes (total plant PC and grass cover GC, plant width density PWD, number of plant patches NPP and plant interdistance PI), soil nutrient contents (organic carbon SOC, total nitrogen TN, and available phosphorus AP) and activities of hydrolase enzymes (β-glucosidase and phosphatase) using multiple linear regressions analysis and structural equation modeling.

The current research reported a strong effect of soil pH and climate factors on vegetation attributes. P values obtained from multiple linear regressions are highly significant for PC (P = 0.0001), GC (P = 0.045), PWD (P = 0.0005), PI (P = 0.039) and NPP (P = 0.007). Soil pH exerted negative effects on all the measured variables. MAP and MAT affected positively and negatively PC, GC and PWD, respectively. Decreased MAP and increased MAT resulted in higher interdistance between plant patches (PI) and consequently the dominance of bare ground areas. NPP may increase with decreasing MAP and MAT suggesting higher frequency of facilitative interactions as resource (water, nutrients) limitation increases.

SEM analysis revealed a negative total effect of soil pH on SOC (β = -0.49), TN (β = -0.69) and AP (β = -0.76) that can be related to its effect on the leaching of dissolved organic carbon and dissolved organic nitrogen, and on the solubility of soil phosphate. Our results reported also a negative effect of soil pH on the activities of the hydrolases β-glucosidase (β = -0.38) and phosphatase (β = -0.3). Climate factors influence the availability of soil nutrients and the activities of hydrolase enzymes. MAP exerted positive effects on SOC (β = 0.73), TN (β = 0.45) and the measured hydrolases (β = 0.57 for β-glucosidase and β = 0.66 for phosphatase). MAP exerted mainly indirect positive control on TN and on the activity β-glucosidase through its effect on SOC. However, MAT is found not a limiting factor on SOC, TN and activities of hydrolases at the temperature range of 15–20 °C. On the contrary, AP was highly controlled by MAT (β = 0.57) but not MAP (β = -0.06). MAT exerted a positive effect on AP probably by increasing soil secondary mineral phosphorus. Based on our findings, we suggest that when MAP is not limiting factor, MAT increases soil AP content. This positive effect can be attributed to the high sand content of the soils (>50%) in Tunisian arid grasslands.

了解控制植被和土壤属性的环境因素对于预测未来气候变化对生态系统功能的影响至关重要。这项研究是沿着干旱梯度在地中海南部草原的10个地点进行的，旨在确定可能影响植被属性（植物总PC和草皮GC，植物宽度）的可能控制因素（平均年降水量MAP，年平均温度MAT和土壤pH）。使用多重线性回归分析和结构分析，密度PWD，植物斑块NPP数量和植物间距PI），土壤养分含量（有机碳SOC，总氮TN和有效磷AP）以及水解酶的活性（β-葡萄糖苷酶和磷酸酶）方程建模。

当前的研究报道了土壤pH和气候因素对植被属性的强烈影响。从多元线性回归获得的P值对于PC（P  = 0.0001），GC（P  = 0.045），PWD（P  = 0.0005），PI（P  = 0.039）和NPP（P = 0.007）。土壤pH值对所有测量变量均产生负面影响。MAP和MAT分别对PC，GC和PWD产生正向和负面影响。MAP的降低和MAT的增加导致植物斑块（PI）之间的距离增加，从而导致裸露的地面区域占主导地位。NPP可能随着MAP和MAT的降低而增加，表明随着资源（水，养分）限制的增加，促进相互作用的频率也更高。

SEM分析表明，土壤pH值对SOC（β= -0.49），TN（β= -0.69）和AP（β= -0.76）的总负面影响可能与其对溶解性有机碳和溶解性碳的浸出的影响有关。有机氮，对土壤磷酸盐的溶解度。我们的结果还报道了土壤pH值对水解酶β-葡萄糖苷酶（β= -0.38）和磷酸酶（β= -0.3）活性的负面影响。气候因素影响土壤养分的可用性和水解酶的活性。MAP对SOC（β= 0.73），TN（β= 0.45）和测得的水解酶（β-葡萄糖苷酶的β= 0.57和磷酸酶的β= 0.66）产生积极影响。MAP通过对SOC的影响，主要对TN和β-葡萄糖苷酶活性起间接间接控制作用。但是，MAT并不是SOC的限制因素，TN和水解酶在15–20°C的温度范围内的活动。相反，AP受MAT（β= 0.57）而不是MAP（β= -0.06）高度控制。MAT可能通过增加土壤中的次生矿物质磷而对AP产生积极影响。根据我们的发现，我们建议当MAP不是限制因素时，MAT会增加土壤AP含量。这种积极的作用可以归因于突尼斯干旱草原土壤的高含沙量（> 50％）。