The serious soil erosion on the Loess Plateau cause the deep cut gullies, fragmentation of
landform and form a complicated landform, thus result in spatial heterogeneity of water and
heat. Then, there are series of adjustments occur on plant community structure, reproductive
strategies, leaf morphological and physiological characteristics to adapt different soil
environments. In this study, the community structures in five soil erosion environments on
slope-gully system (sunny gully slope, sunny hilly slope, hilltop, shady hilly slope, and shady
gully slope) on three vegetation zones (forest zone, forest-steppezone, and steppe zone) on the
hilly-gully region of the Loess Plateau were examined. The species niche breadth and
important value in community were analysed to identify dominant species at different soil
erosion environments. The reprodution, morphology, anatomy, and physiology of seclected
nine dominant species (Artemisia scoparia, Artemisia gmelinii, Artemisia giraldii,
Bothriochloa ischcemum, Stipa bungeana, Phragmites australis, Lespedeza davurica,
Periploca sepium and Sophora davidii) were studied. And, four typical shoot architecture
species (A. gmelinii, with dense shoot architecture; A. giraldii, with expanding shoot
architecture; B. ischaemum, with a tussock-formingshoot architecture; and S. viciifolia, with a
main-stem shoot architecture) was selected to analysis the shape of phytogenic mounds and
its influence of mirco-environmnent on slope. The main results are as follows:
(1) Fom forest to steppe zone, plant community structures become simple, species
diversity decreased, and the number of species showed a slight increased with mesophytes
and phanerophytes decreased, while xerophytes and cryptophytes increased. At different soil
erosion environments on slope-gully system, the variation of species evenness was not
significant. On shady slope, the species diversity and richness were relative larger than sunny
slope. The xerophyte and cryptophytes increased at sunny gully slope. Hilltop had a higher therophyte proportion than the other erosion environments. From sunny to shady gully slope,
the species niche and important value in community decreased with the decreasing of erosion
degree. Xerophyte and xero-mesophytes have a wide range of distribution on the hilly-gully
region of the Loess Plateau.
(2) For same species, single dry weight of inflorescence (flower) and seed mass showed
certain genetic stability, and no significant difference existed in different soil erosion
environments on slope-gully system. At the sunny gully slope and shady gully slope, plant
reproductive investment was low, but the high proportion of cryptophytes on these
environments made vegetation regeneration relying mainly on bud bank. The reproductive
investment of species on hilltop and sunny hilly slope were larger than the other three erosion
environments which result in a large number of seeds and thus was beneficial to the expansion
of seed dispersal plants. L. davurica had a larger reproductive allocation, while two shrubs (P.
sepium and S. davidii) were relatively less. In vegetation turning-green season, the larger
perennial bud bank ensure a rapid vegetation renewal. The larger seasonal bud bank on
fruit-setting season ensure the accumulation of photosynthate.
(3) The leaf morphological and anatomical characteristics at same slope-gully erosion
environment on the three vegetation zones had a slight changes, but these characteristics
showed significant changes at different erosion environments on slope-gully system. With the
increasing of soil erosion degree, leaf thickness, dry matter content, cuticle thickness, palisade
tissue thickness, xylem area/phloem area increased, while leaf area, epidermal cell size,
spongy tissue thickness, intercellular space decreased. In those leaf morphological and
anatomical indices, xylem area, which mediate plant water transportation, had the closest
relationship with plant environmental adaptability. Different plants have its special structure
to adapt the semi-arid climate on the Loess Plateau: water storage parenchyma of A. scoparia,
total-palisade tissue of A. gmelinii, bi-palisade tissue and big bundle sheath cells of A. giraldii
and S. davidii, mucilage cell of L. daurica; special bulliform cells of B. ischcemum and P.
australis; multilayer sclerenchyma of S. bungeana; thick cuticle of P. sepium. From leaf
morphological and anatomical characteristics, comprehensive analysis of the subordinate
function showed that S. bungeana, which has a well developed protective tissues, had the
strongest environmental adaptability.
(4) Similar to plant morphological characteristics, plant physiological indices at same
slope-gully erosion environment on the three vegetation zones showed a slight changes, but
those characteristics presented significant changes at different erosion environments on slope-gully system. From sunny to shady gully slope，with the increasing of soil erosion
degree, the degree of cell damage and amount of chlorophyll destruction increased. But plant
resistance to environmental stress by increasing leaf water-holding ability, osmotic adjustment
substances, stress-resistance enzymes, non-enzymatic antioxidants, meanwhile by decreasing
leaf relative water content and free water/bound water. This processes are at the expense of
plant growth rate to deal with the environmental stress. Among the 21 measured physiological
indices, ascorbic acid oxidase (APX) had the closest relationship with plant environmental
adaptability. From plant physiological indices, comprehensive analysis of the subordinate
function showed that two testing shrubs, S. davidii and P. sepium, had a strong environmental
(5) Different shoot architecture species have different ability of preventing soil erosion
and retaining sediment, thus the shape of phytogenic mound changes with slope gradient
increasing. Mound shapes changed from symmetrical mound-type structures into
asymmetrical terrace-type structures as slope gradient increased, but the change at 0-15°for
S. viciifolia, at 26-35°for A. gmelinii and B. ischaemum, at >35°for A. giraldii. Among the
plant shoot architecture parameters, plant basal diameter along the slope was significantly
correlated with mound height, while the plant basal diameter perpendicular to the slope and
total cross-sectional area of the stem at the plant base were associated with mound area.
Mound height increased with slope for all species, while mound area showed opposite
tendency. The phytogenic mounds can act as ‘resource islands’, thus improved species
richness and stress resistance of plant community on slope. A. giraldii with expanding shoot
architecture and S. viciifolia with its large canopy can create relatively large mounds.
(6) In reproductive strategy, K-reproductive strategyare adopted by A. scoparia, A.
gmelinii, A.giraldii, B. ischcemum and P. sepium; and r-reproductive strategy by S. bungeana,
L. davurica and S. davidii. According to the palnt anatomical and physiological characteristics
of environmental adaptation, the testing plants were divided into three types: I, stress
avoidance, including A. scoparia, S. bungeana and P. australis; II, strain repair, including A.
giraldii, B. ischcemum and L. davurica; III, strain avoidance, A. gmelinii, P. sepium and S.
davidii. Integrative subordinative value was calculated based on reproductive, morphological,
anatomical and physiological characteristics of plant. The integrative subordinative values of
testing plants on different soil erosion environments of slope-gully system were positively
correlated with the species important value in community. From the results of comprehensive
analysis of the subordinate function, two shrubs, S. davidii and P. sepium, showed higher environmental adaptability than another testing plants, followed by widespread plants (A.
gmelinii, L. davurica, S. bungeana), the environmental adaptability of B. ischcemum, A.
giraldii, P. australis, A. scoparia which only distributed on certain erosion environments,
were relatively weak among testing plants.
Key words: community composition; leaf anatomy; plant shoot architecture; reproductive
strategy; stress-resistance physiology; Loess Plateau