Soil gravels and plant
species configuration control vegetation restoration in Qinghai-Tibet
Plateau
Yonggang Youa,b,c, Xinliang Wua,b,c,
Lihe Hana,b,c,Yapei Lua,b,c, Jinxing
Zhoua,b,c*, Ansa Rebia,b,c, Qian
Donga,b,c , Lina Wanga,b,c,
Pengcheng Zhanga,b,c
a.Jianshui Research Station, School of Soil and
Water Conservation, Beijing Forestry University, Beijing 100083, China
b. Key Laboratory of State Forestry
Administration on Soil and Water Conservation, Beijing Forestry
University, Beijing 100083, China
c Engineering Research Center of Forestry
Ecological Engineering, Ministry of Education, Beijing Forestry
University, Beijing 100083, China
* Corresponding author. E-mail:bjfuzix@126.com (J.Zhou).Address: School of Water and Soil Conservation, Beijing
Forestry University, East Qinghua Road No.35 in Haidian District,
Beijing, 100083, China.
Note: Yonggang You and Xinliang Wu contribute equally to this paper.
Abstract: Soil gravel
content strongly affects ecological restoration; however, the response
and mechanism of plant traits to soil gravel content under the sensitive
and fragile natural environment of Qinghai-Tibet Plateau remains
unclear. Herein, soils with three gravel content (10%, 30%, 50%) in
the southeastern Tibetan Plateau were selected, and three plant species
( one indigenous specie of Elymus dahuricus (Ed) , and two
introduced ones of Festuca elata (Fe ) and Medicago
sativa (Ms )) were used in seven planting patterns with different
proportions (Fe , Ed , Ms , Fe +Ed(1:1), Fe +Ms (2:1), Ed +Ms (2:1),Fe +Ed +Ms (2:2:1)). Plant traits, phytochemical
properties and soil stoichiometric characteristics were measured to
explore the interactive effects of soil gravels and plant species on
vegetation restoration. Average plant height, coverage, shoot biomass
and total biomass were most affected by plant species
(F=277~611, p<0.01), followed by gravel
content (F=90~195, p<0.01) and their
interaction (F=5~51, p<0.05); root biomass was
most affected by gravel content (F=130, p<0.01). Among plant
species, shoot and root biomass, total biomass overall decreased in the
order of Fe+Ed+Ms˃Fe˃Fe+Ms˃Fe+Ed˃Ms˃Ms+Ed˃Ed . Plant total
biomass, shoot biomass, root biomass and shoot/root ratio among
different soils overall decreased in the order of low˃ high˃ medium
gravel contents. All plant species were restricted by soil nitrogen
except for Ed and Ed +Ms (N:P>14). In
addition, average plant height, coverage, shoot biomass and total
biomass were separately negatively and positively correlated with bulk
density and total porosity (r=-0.88~-0.96 and
0.78~0.91, p<0.05), so did for total nitrogen,
total phosphorus, organic carbon, C:N and N:P of shoot fraction and
rhizosphere soils (|r|=0.69~0.97,
p<0.05), indicating that gravel content affects plant growth
through bulk density and nutrients. Therefore, optimizing the
configuration of soil properties (mainly nitrogen and compactness) and
plant species (isecologic niche plants) is an effective strategy for
ecological restoration in the Qinghai-Tibet Plateau.
Keywords: Ecological restoration, Soil gravel, Plant species,
Plant biomass, Tibetan Plateau.
Introduction
As the key component of soil texture, the content and distribution of
gravel particles affect soil physical structure and hydrological
processes such as soil water storage, runoff, water infiltration, solute
transport and water flow (Smets et al.,2011; Qiu et al.,2015; Zhang et
al.,2016;Wang et al.,2019; Mahinroosta et al., 2021); they also could
reduce the mechanical resistance to root extension (Alameda et
al.,2012), and may cause root aggregation and growth (Clark et
al.,2003). But the impact and the underlying mechanism of soil gravels
are relatively complex (Han et al.,2021; Li et al.,2020). In order to
better comprehensively unravel the effect of soil on plant growth, the
importance of gravel cannot be ignored (Du et al.,2022).
At present, a large number of studies have shown that gravels could
promote cation exchange, and store water to facilitate plant growth
(Certini et al.,2004). For instance, in the foothills of the Himalayas
mountains, high gravel content of up to 40% can preserve rainwater and
promote better economic benefits for leguminous plants or relatively
drought-tolerant crops with vigorous rootstock systems (Grewal et
al.,1984). Hubbert et al. (2001) reported that in stony soil, gravel in
the soil can provide 70% water for plant growth. Other studies have
found that the addition of a certain amount of waste gravel can improve
soil physical properties, and is conducive to the improvement of soil
quality and crop yield (Ye et al.,2021; Jin et al.,2022). In the arid
area of northwest China, the addition and mulching of appropriate
topsoil gravel can increase the retention of soil moisture (Qiu et
al.,2021) and increase the yield of Malus pumila , Zea maysand other crops (Suo et al.,2019). For the pot culture of flue-cured
tobacco, adding 10%-30% volcanic ash gravel significantly promoted the
plant height and maximum leaf area of the overground part of the initial
flue-cured tobacco, but the influence of volcanic ash gravel on the
growth of tobacco plants became weaker with the extension of planting
time (Shen et al.,2012). Less gravel inhibits the development of tobacco
plants, but is beneficial to the accumulation of dry matter in the later
period, while the opposite is true when gravel content is too high (Luo
et al.,2014).
In general, soil gravel has different effects on plant growth at
different growth stages. The content of gravel in the soil also leads to
a decrease in soil water retention and the lack of root-soil contact
area, and the lack of resources will restrict the growth of plants
(Rytter et al., 2012; Ceacero et al., 2020). Studies on the Loess
Plateau have found that high gravel content (50%) restricts plant
growth and dry matter accumulation (Mi et al., 2016). For grassland in
the Qinghai-Tibet Plateau, gravel content was found to negatively
correlate with above-ground biomass and vegetation coverage (Yu et al.,
2015), and soil organic carbon and total nitrogen reserves were the
highest when gravel was covered by 40-50% (Wang et al., 2011).
Additonally, soil gravel could reduce plant nitrogen and phosphorus
contents, and inhibit plant growth and development (Masoni et al.,
2008). A potted pot study on the adaptation of legume Sandalwood to soil
gravels found that with the increase of gravel content, the root/shoot
ratio of seedlings showed an increasing trend, and the biomass of stems
transferred to roots and leaves, especially to low-grade roots (Liu et
al., 2016). Therefore, the influence of gravel content on plant traits
is species-specific, and the difference response of vegetation to soil
gravels varys in different ecosystems.
Large-scale projects have disturbed soil surface texture and damaged
native vegetation, and if timely ecological restoration is not carried
out, it may cause serious ecological consequences such as land
degradation and water and soil loss (Zhang et al.,2015; Si et al.,2020;
Chen et al.,2020). After the ecological environment is disturbed by
engineering, scientific and effective vegetation restoration is needed
to ensure ecological security (Xie et al.,2021). However, the complex
geological background and unique, sensitive and fragile natural
environment of the Qinghai-Tibet Plateau make ecological restoration
techniques scarce (Zhang et al.,2016b; Xu et al.,2022; Li et al.,2022).
Gravel soils are widely distributed in the Tibetan Plateau (Pan et
al.,2017). Therefore, it is urgent to understand the mechanism of soil
gravel on plant traits to carry out the effective ecological
restoration. The objectives of this study were to: (i) evaluate the
effects of gravel content and plant species on plant growth; (ii)
explore the mechanism of action of gravel content and plant species on
plant growth based on stoichiometry.