摘要:

目的

土壤水分是影響我國北方水分虧缺地區(qū)植被生長的重要因素，探究不同造林密度和水分管理下毛白楊林分的土壤水分狀況，能為華北黃泛平原地區(qū)人工林土壤水分維持提供參考。

方法

以不同造林密度（Ⅲ3 m × 3 m、Ⅱ3 m × 6 m、Ⅰ6 m × 6 m）和水分管理（滴灌FI、雨養(yǎng)NI）下的5種（FIⅢ、FIⅠ、NIⅢ、NIⅡ、NIⅠ）毛白楊林分為研究對象，在2021年生長季內(nèi)（5、6、8和10月），采用烘干稱重法測定各處理6 m剖面內(nèi)的土壤含水量（SWC），研究不同處理土壤水分狀況及土壤干層現(xiàn)象。

結(jié)果

（1）各處理毛白楊林分淺土層（0 ~ 30 cm和30 ~ 100 cm）的SWC（5.62% ~ 15.53%）顯著低于深土層（100 ~ 200 cm、200 ~ 400 cm和400 ~ 600 cm）（16.50% ~ 27.00%）；林分SWC在0 ~ 240 cm垂直剖面內(nèi)隨深度增加而增加，并在240 ~ 260 cm（26.37% ~ 30.56%）和360 ~ 400 cm（22.79% ~ 33.00%）出現(xiàn)兩個(gè)峰值，而400 ~ 600 cm變化平緩；（2）5種林分土壤均在10月最為濕潤，平均SWC為20.16% ~ 23.16%；雨養(yǎng)條件下，不同密度毛白楊林分在6月最干燥，平均SWC為13.11% ~ 14.96%，滴灌減輕了30 cm以下土層SWC的季節(jié)變異程度；（3）不同水分管理下，高密度林分中深土層土壤水分狀況最好（FIⅢ和NIⅢ深土層平均SWC分別為23.18%和21.13%），但雨季末（10月），NIⅡ土壤水分補(bǔ)償量最高，達(dá)403.12 mm。在高密度和低密度林分中滴灌顯著提高了林分0 ~ 30 cm土層的SWC，且增加了深土層土壤水分補(bǔ)償量（FIⅢ較NIⅢ和FIⅠ較NIⅠ的儲水量變化量分別提高了84.40%和173.99%），滴灌僅顯著提高了高密度林分土壤儲水量（P < 0.05）；（4）滴灌和降雨均能緩解或消除不同密度林分在2 m深度內(nèi)出現(xiàn)的可恢復(fù)性土壤干層現(xiàn)象。

結(jié)論

根據(jù)本研究結(jié)果，建議在華北黃泛平原毛白楊大徑材林培育過程中，以3 m × 3 m密度造林且于旱季（4—6月）輔以多頻率滴灌充分灌溉，促進(jìn)楊樹人工林在快速生長期（2 ~ 4年）的林木生長并改善其深層土壤水分狀況。待林分出現(xiàn)密度效應(yīng)及深層土壤水消耗后，可通過間伐等措施在實(shí)現(xiàn)土壤水分維持的同時(shí)提高楊樹人工林林地生產(chǎn)力。

Abstract:

Objective

In water-deficit area of northern China, soil water content is a crucial factor affecting plant growth. Studying the soil water status of Populus tomentosa stands under different planting densities and water treatments can provide a reference basis for soil water maintenance of plantations in the North China Plain.

Method

Populus tomentosa plantations under five different planting densities (Ⅲ 3 m × 3 m, Ⅱ 3 m × 6 m and Ⅰ 6 m × 6 m) and water (drip irrigation, FI and rainfed, NI) treatments (FIⅢ, FIⅠ, NIⅢ, NIⅡ and NIⅠ) were selected in this study. During the growing season (May, June, August and October) in 2021, soil water content (SWC) within the 6 m-depth soil profile was measured using the drying-weighing method, soil water content conditions and the occurrence of dry soil layer (DSL) were investigated and compared among different treatments.

Result

(1) Shallow soil layers (0?30 cm and 30?100 cm, ranging from 5.62% to 15.53%) showed significantly lower SWC than the deep soil layers (100?200 cm, 200?400 cm, and 400?600 cm, ranging from 16.50% to 27.00%) in each treatment. The SWC in all stands increased with depth within the vertical profile of 0?240 cm, showing two peaks at 240?260 cm (26.37%?30.56%) and 360?400 cm (22.79%?33.00%), while the change of SWC at 400?600 cm was relatively gradual. (2) All five stands exhibited the highest soil water availability in October, with an average SWC from 20.16% to 23.16%. In rainfed treatment, soil was driest in June independent of planting density, the average SWC ranged from 13.11% to 14.96%. Drip irrigation treatment reduced the seasonal variation in SWC in the soil layer below 30 cm. (3) Under different water treatments, high density stands exhibited the highest soil water availabilities in the deep soil layers (average SWC of 23.18% for FIⅢ and 21.13% for NIⅢ). However, NIⅡ exhibited the highest soil water compensation at the end of the rainy season (October) of 403.12 mm. In both high and low density stands, SWC in the 0?30 cm soil layer was significantly increased by drip irrigation treatment, the compensation of soil water in the deep layers was also enhanced (the change in water storage was 84.40% in FIⅢ than in NIⅢ, and 173.99% higher in FIⅠ than in NIⅠ). Drip irrigation treatment only significantly improved soil water storage in high density stands (P < 0.05). (4) Both drip irrigation and precipitation effectively alleviated or eliminated the occurrence of recoverable DSL within 2 m-depth under different planting densities.

Conclusion

According to the results of this study, a 3 m × 3 m planting density with frequent full irrigation treatment during dry season (April to June) is recommended for the cultivation of large-diameter poplar plantation in the North China Yellow River Plain in order to achieve fast tree growth in the early growing stage (2?4 years) and improve water condition of the deep soil layers. After the occurrence of evident density effect and deep soil water content depletion, management practices like thinning can be implemented to maintain soil water production and enhance the productivity of poplar plantations.

圖  1   試驗(yàn)林不同深度土壤田間持水量實(shí)測值與模擬值比較

Figure  1.   Comparison of measured and simulated field capacity in experimental forest under different depths

圖  2   不同密度和水分管理下細(xì)根根長密度的二維空間分布

Figure  2.   Two-dimensional spatial distribution of root length density (RLD) under different densities and water treatments

圖  3   不同密度和水分管理下土壤含水量的二維空間分布

*代表該土層深度不同水平距樹距離處土壤含水量差異顯著（P < 0.05）。* indicates significant differences (P < 0.05) in soil water content at different horizontal distances from tree base in the same soil layer.

Figure  3.   Two dimensional spatial distribution of soil water content under different densities and water treatments

圖  4   不同密度和水分管理中各土層的平均土壤含水量

不同小寫字母代表不同土層SWC差異顯著（P < 0.05），不同大寫字母代表不同處理SWC差異顯著（P < 0.05）。Different lowercase letters indicate significant differences in SWC among soil layers(P < 0.05), and uppercase letters indicate significant differences in SWC among treatments (P < 0.05).

Figure  4.   Average soil water content in each soil layer under different densities and water treatments

圖  5   2021年5—10月不同密度和水分管理各土層土壤含水量時(shí)間動態(tài)變化

Figure  5.   Temporal dynamics of soil water content in each soil layer under different densities and water treatments from May to October in 2021

圖  6   不同密度和水分管理土壤儲水量

不同小寫字母代表不同處理土壤儲水量差異顯著（P < 0.05）。Different lowercase letters indicate significant differences in soil water storage among treatments (P < 0.05).

Figure  6.   Soil water storage under different densities and water treatments

圖  7   2021年5—10月不同密度和水分管理下土壤儲水量變化量

土層深度0 ~ 6 m每20 cm采集一組數(shù)據(jù)。Data were collected every 20 cm at soil 0 to 6 m depth.

Figure  7.   Variations of soil water storage variation under different densities and water treatments from May to October in 2021

圖  8   不同密度和水分管理下不同土層深度內(nèi)土壤干層現(xiàn)象

Figure  8.   Phenomenon of dry soil layer (DSL) in different soil depths under different densities and water treatments

表  1   2021年不同密度和水分處理林分基本情況

Table  1   Basic information of stands under different densities and water treatments in 2021

處理
Treatment 平均胸徑
Average DBH/cm 平均樹高
Average tree height/m 林分蓄積量/（m3·hm?2）
Stand volume /（m3·ha?1） 林地生產(chǎn)力/（m3·hm?2·a?1）
Forest land productivity /（m3·ha?1·year?1） FIⅢ 14.57 ± 0.55ab 15.65 ± 0.44a 119.1 ± 11.12a 36.61 ± 3.60a FIⅠ 15.49 ± 0.50a 12.55 ± 0.15b 15.28 ± 1.15b 6.94 ± 0.30c NIⅢ 12.92 ± 0.87b 15.33 ± 0.40a 92.32 ± 13.25b 25.58 ± 4.64b NIⅡ 14.79 ± 0.81ab 14.78 ± 0.79a 58.74 ± 8.10c 21.20 ± 4.12b NIⅠ 14.48 ± 0.74ab 12.47 ± 1.04b 13.38 ± 2.21c 5.76 ± 1.30c 注：NI.雨養(yǎng)；FI.滴灌。不同小寫字母表示同列不同處理間差異顯著（P < 0.05）。Notes: NI, rainfed; FI, drip irrigation. Different lowercase letters in the same column indicate significant differences among different treatments (P < 0.05).

表  2   試驗(yàn)地的土壤物理性質(zhì)

Table  2   Soil physical characteristic of the experimental site

土層
Soil layer/cm顆粒組成 Soil particle size distribution/%質(zhì)地
Soil texture土壤密度
Bulk density/（g·cm?3） 砂粒 Sand粉粒 Silt黏粒 Clay 0 ~ 4051.9642.185.85砂壤土 Sand loam1.37 40 ~ 46024.2767.907.83粉壤土 Silt loam1.49 460 ~ 60056.8237.755.43砂壤土 Sand loam1.63

表  3   不同密度和水分管理下各土層的平均細(xì)根根長密度

Table  3   Average RLD in each soil layer under different densities and water treatments m/m3

處理 Treatment 土層 Soil layer/cm 0 ~ 30 30 ~ 100 100 ~ 200 200 ~ 400 400 ~ 600 FIⅢ 1 971.67 ± 456.97Aa 1 264.15 ± 447.82Aab 451.71 ± 176.84Bb 346.52 ± 118.01Ab 121.12 ± 16.11Ab FIⅠ 6 997.50 ± 866.28Aa 836.25 ± 165.36Ab 171.17 ± 46.57Bb 270.52 ± 26.22Ab 298.40 ± 70.30Ab NIⅢ 4 686.82 ± 331.50Aa 3 119.27 ± 2 065.69Aa 1 223.86 ± 94.34Aa 404.95 ± 47.77Aa 415.24 ± 45.14Aa NIⅡ 5 828.61 ± 723.29Aa 1 199.00 ± 199.47Ab 673.68 ± 51.98ABb 422.52 ± 75.87Ab 410.43 ± 93.22Ab NIⅠ 4 452.10 ± 3 850.95Aa 1 365.34 ± 580.03Aa 473.06 ± 191.01Ba 398.97 ± 124.32Aa 188.02 ± 17.11Aa 注：不同大寫字母表示同列不同處理間差異顯著（P < 0.05），不同小寫字母表示同行不同土層間差異顯著（P < 0.05）。Notes: different uppercase letters in the same column indicate significant differences among different treatments (P < 0.05), and different lowercase letters in the same row indicate significant differences among varied soil layers (P < 0.05). [1]

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