六盘山半干旱区华北落叶松林坡面土壤含水量的降雨响应

doi:10.13866/j.azr.2023.04.08

摘要/Abstract

摘要：

在宁夏六盘山外围半干旱区，土壤含水量是影响林木成活与生长的关键因子，需深入理解森林坡面不同坡位的土壤含水量对降雨量的响应差异。本文在宁夏六盘山叠叠沟小流域，选择一个华北落叶松人工林典型坡面，于2021年5—10月利用自动气象站和土壤水分仪连续监测降雨等气象条件和坡面土壤含水量变化，分析土壤含水量的坡位差异及对降雨量级的响应。观测期间总降水量为443.7 mm，虽然接近多年平均值，但夏季干旱严重。结果表明：（1）土壤含水量存在明显的生长季内变化，整体表现为先降低后升高的趋势，8月最低（0.112 m³·m^-3）。（2）土壤含水量存在明显的坡位差异，整体表现为：上坡[（0.191±0.044） m³·m^-3]>中坡[（0.158±0.045） m³·m^-3]>下坡[（0.146±0.034) m³·m^-3]，表明土壤含水量的坡位变化因处于干旱年，主要受植被蒸散耗水量大小的影响，而受坡面汇流影响不大。（3）在同一降雨量级时，因受土壤孔隙度和持水能力、林下草本截持、优先流等的影响差异，中坡的土壤含水量对降雨量增加的响应最敏感，其次是上坡，下坡最不敏感。（4）在本研究区，降雨以<10 mm的小降雨事件为主，7 mm是形成有效降雨的阈值，超过此阈值的降雨才有可能缓解0~20 cm土层土壤干旱和补给该层土壤水分。本研究有助于理解半干旱山区森林坡面的土壤含水量大小变化与分布特征，指导确定基于坡面土壤水分的植被承载力和进行林水综合管理。

关键词: 半干旱区, 六盘山, 华北落叶松, 土壤含水量, 坡位差异, 降雨补给

Abstract:

In the semi-arid zone of the Liupan Mountains in Ningxia, soil water content is a key factor affecting the survival and growth of trees, and it is necessary to understand the differences in soil water content on different slope positions of forested slopes and their response to different rainfall amounts. For this purpose, a typical slope covered by Larix principis-rupprechtii plantations was selected in the small watershed of Diediegou in the Liupanshan Mountains. From May to October 2021, meteorological conditions (such as precipitation) and changes in soil water content on this slope were continuously monitored with automatic weather stations and soil moisture meters to analyze the differences in soil water content on the slopes and their response to the depth of individual rainfall events. The total precipitation depth during the monitoring period was 443.7 mm, which was close to the long-term annual average, but with severe drought in summer. The results showed the following: (1) The soil water content varied significantly within the growing season; the overall level first decreased and then increased, being the lowest in August (0.112 m³·m^-3). (2) There were clear differences in soil water content among slope positions, generally in the order upper slope [(0.191 ± 0.044) m³·m^-3] > middle slope [(0.158 ± 0.045) m³·m^-3] > lower slope [(0.146 ± 0.034) m³·m^-3]. This indicated that the main factor influencing the differences in soil water content along slope positions is the amount of evapotranspiration by forest/vegetation, rather than the redistribution of rainwater along the slope by slope runoff in this dry year. (3) To the same rainfall depth, the response of soil water content on the middle slope was the most sensitive, followed by that on the upper slope, and the lower slope was the least sensitive, owing to the integrated effects of soil porosity, water-holding capacity, and understory vegetation. (4) At the study site, rainfall was dominated by small rainfall events below 10 mm, with 7 mm representing the threshold for effective rainfall, above which the rainfall is likely to alleviate the soil dryness and recharge the soil moisture in the soil layer of 0-20 cm. The results of this study can aid understanding of the variation and spatial distribution of soil water content on forest slopes in semi-arid mountainous areas and help determine the water-carrying capacity of forest/vegetation and integrated

Key words: semi-arid zone, Liupan Mountains, Larix principis-rupprechtii, soil water content, slope position difference, soil moisture recharge by rainwater

石建周, 刘贤德, 田青, 于澎涛, 王彦辉. 六盘山半干旱区华北落叶松林坡面土壤含水量的降雨响应[J]. 干旱区研究, 2023, 40(4): 594-604.

SHI Jianzhou, LIU Xiande, TIAN Qing, YU Pengtao, WANG Yanhui. Rainfall response of soil water content on a slope of Larix principis-rupprechtii plantation in the semi-arid Liupan Mountains[J]. Arid Zone Research, 2023, 40(4): 594-604.

图/表 9

表1

表2

不同坡位样地0~100 cm土层的土壤物理性质"

坡位	土层深度/cm	土壤容重 /（g·cm^-3）	土壤饱和持水率/%	土壤毛管持水率/%	土壤田间持水率/%	非毛管孔隙度/%	毛管孔隙度/%	饱和导水率 /（mm·min^-1）
上坡	0~10	0.89±0.05c	71.55±7.48a	52.41±1.45ab	49.23±1.88a	16.81±4.71a	46.57±2.11ab	1.22±0.64a
	10~20	0.96±0.02c	65.29±2.51a	55.16±8.88a	49.52±4.75a	9.82±7.75ab	52.75±7.39a	1.36±0.54a
	20~40	1.09±0.07b	51.48±5.83b	45.55±2.72bc	42.53±2.05b	6.29±4.46b	49.57±2.52ab	0.94±0.12a
	40~60	1.10±0.07b	49.63±5.76b	40.43±2.44cd	38.12±2.41b	9.99±3.40ab	44.53±0.69b	1.16±0.33a
	60~80	1.25±0.02a	40.27±1.40c	35.91±2.76d	32.64±2.05c	5.44±2.91b	44.96±3.58b	0.92±0.26a
	0~80	1.11±0.14b	50.66±12.31b	42.16±8.42c	39.14±7.54b	9.01±4.01ab	46.14±3.87ab	1.12±0.19a
中坡	0~10	0.94±0.05d	66.22±4.18a	53.78±2.91a	51.17±3.24a	11.64±0.64a	50.42±0.67a	1.58±0.70a
	10~20	1.06±0.12c	55.15±9.97b	42.11±4.40b	39.94±4.54b	13.23±6.24a	44.20±3.15b	1.58±0.48a
	20~40	1.08±0.01bc	52.35±1.85bc	42.09±2.46b	38.84±2.12b	11.09±0.84a	45.45±2.07ab	1.72±0.79a
	40~60	1.11±0.03bc	49.99±4.06bc	40.25±4.46b	38.32±4.51b	10.77±2.79a	44.56±4.22b	1.71±1.12a
	60~80	1.20±0.07ab	43.15±5.25cd	34.93±1.45cd	32.84±0.41cd	9.59±5.69a	41.82±3.15b	1.12±0.20a
	80~100	1.27±0.07a	38.66±4.56d	32.74±1.29d	30.66±1.46d	7.25±6.26a	41.48±3.31b	1.04±0.29a
	0~100	1.13±0.11bc	48.97±9.65bc	39.59±7.37bc	37.24±7.16bc	10.23±2.03a	44.12±3.23b	1.46±0.30a
下坡	0~10	0.93±0.05c	66.53±7.30a	54.34±11.36a	47.15±10.99a	11.46±8.14a	50.51±8.46a	5.29±5.93a
	10~20	1.02±0.04bc	57.63±4.56ab	54.15±3.73a	47.62±4.37a	3.53±1.51a	55.31±2.15a	3.50±2.97a
	20~40	1.06±0.02b	52.33±2.67bc	44.77±7.33ab	38.85±6.30ab	8.09±5.24a	47.34±6.73a	4.09±3.60a
	40~60	1.09±0.07ab	51.41±5.70bc	45.53±5.48ab	39.24±5.08ab	6.25±6.12a	49.44±5.34a	3.14±1.82a
	60~80	1.13±0.12ab	48.43±10.64bc	42.48±8.90ab	36.99±8.38ab	6.56±3.01a	47.26±4.85a	2.37±2.15a
	80~100	1.18±0.02a	43.95±2.09c	39.45±2.42b	34.55±2.88b	5.24±5.15a	46.67±3.79a	1.49±0.86a
	0~100	1.09±0.09ab	51.64±7.87bc	45.29±6.15ab	39.40±5.42ab	6.73±2.71a	48.72±3.24a	3.31±1.33a

表2

图1

图2

表3

图3

图4

图5

图6

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样地	坡度 /（°）	坡位	海拔 /m	林龄 /a	密度 /（株·hm^-2）	林冠郁闭度	平均胸径/cm	平均树高/m	平均枝下高/m	平均冠幅/m	草本总盖度/%	草本生物量 /（t·hm^-2）	枯落物层厚度 /cm	枯落物生物量 /（t·hm^-2）
H1	28	上坡	2145	32	1550	0.69	11.33± 3.17a	7.76± 1.82a	2.05± 0.79b	3.02± 0.80a	70±5b	2.36± 0.20c	3.25± 0.31ab	9.82± 1.15ab
H2	24	中坡	2090	32	1750	0.73	10.89± 3.46a	7.84± 2.29a	2.76± 1.26a	3.01± 1.02a	75±6b	2.99± 0.24b	4.00± 0.32a	12.04± 1.48a
H3	34	下坡	2040	32	2075	0.82	9.91± 4.42a	7.83± 2.63a	2.09± 1.42ab	2.72± 1.05a	95±3a	6.19± 0.16a	3.13± 0.28b	7.82± 0.65b

坡位	平均土壤含水量/（cm³·cm^-3）
坡位	0~10 cm	10~20 cm	20~40 cm	40~60 cm	0~60 cm
上坡	0.136±0.042Da	0.178±0.04Ca	0.215±0.061Ba	0.236±0.049Aa	0.191±0.044a
中坡	0.112±0.037Dc	0.145±0.04Cb	0.178±0.048Bb	0.197±0.055Ab	0.158±0.045b
下坡	0.115±0.043Cb	0.142±0.04Bc	0.141±0.031Bc	0.185±0.039Ac	0.146±0.034c