黄土高原林下草地对模拟增温的短期响应

Abstract

气候变暖在高海拔山地更为明显，山地植被对气候变暖响应的空间格局将成为山地研究新的热点。在黄土高原东部沿纬度梯度选择北段管涔山、中段关帝山和南段五鹿山，分别划分高、中、低3个海拔梯度，每一梯度用开顶式生长室设置对照（CK）、低度增温（LW）、高度增温（HW）3种模拟增温样地，于增温1年后植被生长季调查山地林下草本群落的生长特征及水热因子，探究黄土高原林下草地对气候变暖的短期响应及其随纬度、海拔的变化格局。结果表明：在LW和HW处理下，（1）空气温度增加0.47℃和1.00℃，空气湿度增加1.37%和1.94%，其中空气温度增幅随海拔增加显著增大（P=0.012）；（2）土壤水分减小0.32%和0.64%，土壤温度减小0.07℃和增加0.06℃，其中土壤温度增幅随纬度增加显著减小（P=0.003）；（3）植物密度增加41.27株/m²和78.53株/m²，植物高度增加0.04 m和0.03 m，植物频度增加5.47%和3.47%，而植物盖度显著增加5.32%和0.88%（P=0.042）；（4）植被与温度关系的相关系数绝对值增加31.49%和56.82%，与水分关系的相关系数绝对值增加38.67%和62.89%。因此，山地温度对增温响应更大，且空气温度具正向海拔依赖性，土壤温度具负向纬度依赖性；增温加强植被与水分的关系，促进植物对水的依赖性，进而显著影响植物盖度。然而，增温的短期效应易受到降雨条件的影响，使结果出现误差，故在类似的研究中建议加强试验的时间尺度。;Climate warming is more obvious in high-altitude mountains, and as a result, investigating the spatial patterns of mountainous vegetation responses to climate warming is becoming a new hot spot of mountain research. The Luliang Mountain Range lies on the east side of the Loess Plateau in central China and is characterized by an extremely fragile environment due to the lack of precipitation. Based on latitudinal gradients from north to south in the Luliang Mountain Range, the affiliated Guancen Mountain in its northern section, Guandi Mountain in its central section, and Wulu Mountain in its southern section were selected as study area. Each of these mountains was divided into three gradients: high altitude, medium altitude, and low altitude. The corresponding elevations for the high, medium, and low altitudes were 2571.3 m, 2395.0 m, and 2222.4 m for Guancen Mountain, 2179.1 m, 2000.7 m, and 1899.7 m for Guandi Mountain, and 1602.0 m, 1458.6 m, and 1318.0 m for Wulu Mountain, respectively. Three experimental plots heated by open-top chambers (OTCs) were placed within each altitudinal gradient. Treatments were implemented using completely randomized block design and including control (CK), low temperature increase (LW), and high temperature increase (HW). During the growing season in 2017, the growth characteristics and hydrothermal factors of the herbaceous communities in mountainous forests were surveyed in order to explore the responses of herbaceous communities to climate warming as well as the spatial pattern changes of these responses with latitudinal and altitudinal gradients. The results revealed the following under the LW and HW treatments: (1) air temperature increased by 0.47℃ and 1.00℃, respectively. The atmospheric relative humidity increased by 1.37% and 1.94%, respectively. The increasing amplitude of air temperature grew significantly with altitude (P = 0.012). (2) Corresponding soil moisture decreased by 0.32% and 0.64%, respectively. The soil temperature decreased by 0.07℃ and increased by 0.06℃. The increasing amplitude of soil temperature diminished significantly with latitude (P = 0.003). (3) The respective vegetation density increased by 41.27 plants/m² and 78.53 plants/m², but vegetation height increased by 0.04 m and 0.03 m. The vegetation frequency increased by 5.47% and 3.47%, while vegetation coverage significantly increased by 5.32% and 0.88% (P = 0.042). (4) The relationships among vegetation indices, temperature factors, and moisture factors using RDA ordination analysis indicated that the absolute value of the correlation coefficient between vegetation and temperature increased by 31.49% and 56.82%, as well as that between vegetation and moisture correspondingly increased by 38.67% and 62.89%, respectively. Therefore, in the Luliang Mountain Range, temperature factors were more responsive to warming, with air temperature being positively correlated with altitude and soil temperature being negatively correlated with latitude. However, the warming effects from the OTCs strengthened the relationship between vegetation and moisture, which promoted the dependence of plants on moisture, thereby significantly affecting vegetation coverage. Warming should be controlled in terms of amplitude, which will then have positive effects on vegetation. When precipitation occurred during the experiment, however, the associated moisture enhancement could weaken the warming effects on the soil. Thus the soil temperature decreased during warming treatments, indicating that precipitation had a greater influence on warming effects in regions where precipitation dominated the environmental factors. Therefore, the effects of short-term warming were affected largely by rainfall, which introduced errors into the results. We strongly suggest that the experimental duration should be prolonged in similar studies on warming effects in order to reduce these errors.