Soil Cover Improves Soil Quality in a Young Walnut Forest in the Sichuan Basin, China
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Soil Cover Improves Soil Quality in a Young Walnut Forest in the Sichuan Basin, China Liehua Tie1,2,3,4, Maosong Feng1,2,*, Congde Huang1,2, Josep Peñuelas3,4, Jordi Sardans3,4, Wenyu Bai1,2, Dongmiao Han1,2,5, Tao Wu1,2 and Wenbing Li1,2,6 1 National Forestry and Grassland Administration Key Laboratory of Forest Resources Conservation and Ecological Safety on the Upper Reaches of the Yangtze River, College of Forestry, Sichuan Agricultural University, 611130 Chengdu, China; [email protected] (L.T.); [email protected] (C.H.), [email protected] (W.B.); [email protected] (D.H.); [email protected] (T.W.); [email protected] (W.L.) 2 Sichuan Province Key Laboratory of Ecological Forestry Engineering on the Upper Reaches of the Yangtze River, College of Forestry, Sichuan Agricultural University, 611130 Chengdu, China 3 CSIC, Global Ecology Unit CREAF-CSIC-UAB, Edifici C, Universitat Autònoma de Barcelona, Bellaterra, 08193 Barcelona, Catalonia, Spain; [email protected] (J.P.); [email protected] (J.S.) 4 CREAF, Cerdanyola del Vallès, 08193 Barcelona, Catalonia, Spain 5 Forest Research Institution of Zhaoqing, Guangdong, 526020 Zhaoqing, China 6 Natural Resources and Planning Bureau of Yanjiang District, Sichuan, 641300 Ziyang, China * Correspondence: [email protected]; Tel.: +86-0288-629-1456 Received: 26 January 2021; Accepted: date; Published: date 1 Supplementary tables and figures Table S1 Composition (%) of the number of soil faunal individuals in the soil cover treatments. Composition (%) Groups WF BF SN MS CK Nematoda Secernentea 19.0+++ 20.1+++ 24.8+++ 21.6+++ 17.0+++ Adenophorea 23.3+++ 19.4+++ 35.8+++ 16.0+++ 29.4+++ Arthropoda Arachnida Monosphyronida 0.3+ 0.2+ 0.3+ Araneomorphae 1.1++ 0.6+ 0.8+ Mesostigmata 1.1++ 4.7++ 2.5++ 0.8+ 2.6++ Prostigmata 17.2+++ 21.9+++ 12.0+++ 19.4+++ 17.0+++ Oribatida 8.0++ 8.5++ 6.1++ 8.1++ 4.3++ Protura Eosentomidae 0.3+ 0.8+ 0.4+ Onychiuridae 3.4++ 1.1++ 5.9++ 4.3++ Sminthuridae 6.0++ 6.0++ 2.1++ 4.9++ 4.3++ Isotonfidae 3.4++ 0.9+ 1.9++ 2.2++ Entomobryide 3.6++ 1.0++ Poduridae 1.7++ 5.3++ 1.5++ 3.8++ Insecta Sphaeropsocidae 0.3+ 0.6+ 0.2+ 0.3+ 1.3++ Liposcelididae 0.3+ 0.3+ 0.2+ Phlaeothripidae 0.9+ 0.9+ 0.6+ 1.0++ 0.4+ Cicindelidae 3.4++ 4.1++ 2.5++ 2.2++ 3.0++ Carabidae 1.7++ 2.1++ 0.5+ Staphylinidae 4.9++ 4.1++ 1.9++ 2.9++ 5.1++ Chrysomelidae larvae 0.3+ 0.2+ 0.8+ Limnebiidae 2.9++ Ptinidae 1.7++ 0.9+ 0.6+ 1.5++ 1.3++ Eucleidae 0.9+ 0.3+ 1.1++ 0.8+ Formicidae 0.9+ 0.9+ 0.6+ 3.4++ 6.0++ +++dominant; ++common; + rare. WF: white film; BF: black film; SN: shade netting; MS: maize straw; and CK: control. Values are the averages of three plot replicates during the 27-month study period. 2 Table S2 Eigenvalues, variance explained, and eigenvectors from the first three principal components (PC1, PC2, and PC3) of a principal component analysis (PCA) based on the full set of variables during the 27-month study period. Variable PC1 PC2 PC3 SOM (g kg-1) 0.658 0.414 0.097 Total N (g kg-1) 0.546 -0.689 0.156 Available N (mg kg-1) 0.614 -0.341 -0.037 Total P (g kg-1) 0.510 -0.509 0.008 Available P (mg kg-1) 0.517 -0.459 0.247 Total K (g kg-1) 0.495 0.123 0.553 Available K (mg kg-1) 0.015 0.348 0.831 pH -0.439 0.480 0.152 N 0.825 0.295 -0.196 S 0.643 0.648 -0.146 MBC (mg kg-1) 0.791 0.371 -0.282 Eigenvalue 3.79 2.24 1.26 Variance explained (%) 34.5 20.4 11.4 Values in red correspond to eigenvectors with > 90% of the maximum weight per PC. SOM: soil organic matter; N: number of soil faunal groups; S: number of soil faunal individuals; and MBC: microbial biomass carbon. n=1485. 3 Table S3 Association between principal component analysis eigenvectors of the six selected variables (Pearson’s r) during the 27-month study period. Variable SOM (g kg-1) Total N (g kg-1) Available K (mg kg-1) N S Total N (g kg-1) 0.177 Available K (mg kg-1) 0.236 -0.112 N 0.503 0.217 -0.060 S 0.632 -0.093 0.132 0.720 MBC (mg kg-1) 0.562 0.094 -0.057 0.794 0.724 Value in red is Pearson’s r > 0.750. SOM: soil organic matter; N: number of soil faunal groups; S: number of soil faunal individuals; and MBC: microbial biomass carbon. n=810. 4 Table S4 Summary statistics during the 27-month study period for the minimum number of soil variables required for soil quality assessment. Variable n Minimum Maximum Mean Standard deviation SOM (g kg-1) 135 11.7 90.7 32.5 16.8 Total N (g kg-1) 135 0.574 2.64 1.68 0.402 Available K (mg kg-1) 135 37.1 296 101 36.7 S 135 3.00 41.0 16.1 9.23 MBC (mg kg-1) 135 205 1245 642 229 SOM: soil organic matter; S: number of soil faunal individuals; and MBC: microbial biomass carbon. 5 400 35 350 30 300 25 ) 250 ℃ 20 200 15 150 Rainfall (mm) Rainfall 10 ( Temperature 100 50 5 0 0 Date Figure S1. Rainfall (bars) and soil temperature (line plot) in the 0-5 cm soil layer from May 2013 to April 2015. 6 WF BF SN MS CK WF BF SN MS CK 90 Treatment: P = 0.0002 14 Treatment: P = 0.4078 a (b) Time: P = 0.0000 80 (a) Time: P = 0.0000 12 Treatment × Time: P = 0.0001 70 abab aTreatment × Time: P = 0.0000 ) 10 a a a a a a a 1 a aa ab a a aaaa aaa aaaa aaa aaa aaa ab aa a - 60 a a a aa b a aa aaa a 50 aab b pH 8 a aba bc ab c aa aa 40 b oil 6 bc ab c bc ab 30 a ab b c ab S c bc d bb b b 4 20 b c c ab 2 SOM (g kg (g SOM 10 0 0 3 6 9 12 15 18 21 24 27 3 6 9 12 15 18 21 24 27 Time (Month) Time (Month) ) WF BF SN MS CK 1 3.0 Treatment: P = 0.1997 - 200 Treatment: P = 0.0032 WF BF SN MS CK Time: P = 0.0000 a a a (d) b ) (c) a a Time: P = 0.0000 1 2.5 a a a a - Treatment × Time: P = 0.0000 aaa a aa ab 150 a a a a a a abab b Treatment × Time: P = 0.0000 a 2.0 aa a a ab b aa a a aaa a a a b b ab a aaaa ab ab a a aa bb ab 1.5 ab 100 ab b a aa b b b b b b b b abab b abab a b b a aa c 1.0 bc a bc c 50 Total N (g kg N (g Total 0.5 0.0 kg (mg N Available 0 3 6 9 12 15 18 21 24 27 3 6 9 12 15 18 21 24 27 Time (Month) Time (Month) WF BF SN MS CK 1.0 Treatment: P = 0.6040 WF BF SN MS CK ) 80 a a 1 Treatment: P = 0.0383 a a - a Time: P = 0.0000 aa a ab ) a Time: P = 0.0000 a ab 1 (e) b (f) a - 0.8 Treatment × Time: P = 0.0000 b a a a bb 60 Treatment × Time: P = 0.0000 ab aa ab b a aaa a a ab a a a a a a 0.6 a ab a a a a aa ab ab b a a aaaa 40 a ab a b ab a a ab 0.4 a b ab a a bc a a a a aa a a a b b b b 0.2 20 aaa bc c a a Total P (g kg P(g Total a 0.0 kg (mg P Available 0 3 6 9 12 15 18 21 24 27 3 6 9 12 15 18 21 24 27 Time (Month) Time (Month) WF BF SN MS CK Treatment: P = 0.0000 25 Treatment: P = 0.0000 WF BF SN MS CK ) 250 a 1 - ) Time: P = 0.0000 (h) Time: P = 0.0000 1 a ab - (g) a 20 Treatment × Time: P = 0.0000 a 200 Treatment × Time: P = 0.0000 a a a a a a aa a ba a ab ab 15 aaa aa a a a a aa ab 150 a ab bc b b a ab b b b ab b ab ab bc a ab b b a b c a ab bbab bc b bc cbc c c 10 bc c b b c 100 c bc c a b bc a c c d aab a bcc c c b d Total K kg K (g Total 5 50 0 kg (mg K Available 0 3 6 9 12 15 18 21 24 27 3 6 9 12 15 18 21 24 27 Time (Month) Time (Month) Figure S2.