Based on the field investigation and monitoring, the influences of different
disturbances on the above-ground vegetation characteristic and the below-ground soil
properties were studied in the typical steppe of Loess region. We divided different
plots of treatments into four types: enclosure (E), enclosure plus fertilization (EF),
enclosure plus burning (EB) and grazing (G), which has the same soil type,
topography and hydrothermal conditions. Our results showed that:
1) The dominant vegetation community type of grazing plots is
Agropyron cristatum + Potentilla acaulis +Artemisia sacrorum due to long-term
grazing. The dominant vegetation community type of exclusion of grazing plots is
Stipa grandis + Poa sphondylodes + Medicago ruthenica due to fencing utilization.
The dominant vegetation community type of fertilization plots is Carex duriuscula +
Stipa bungeana + Stipa grandis. The dominant vegetation community type of burning
plots is Artemisia sacrorum + Stipa bungeana + Stipa grandis.
2) The total plant coverage, height and above-ground biomass of different
disturbance manners is that EF>EB>E>G, and the community density of different
disturbance manners is that E>EF>EB>G. Community richness index (R and Ma)
showed a certain tendency within these four treatments: G>EF>EB>E, and
community evenness index (Jsw and Ea) was in an order of E>G>EB>EF. Meanwhile,
the order of diversity index (H and D) was as follows: G>E>EB>EF, while
dominance index showed an opposite tendency.
3) The soil physical properties in the four different disturbances were as follows:
In the 0~50 cm soil layer, the soil bulk density increased with soil depth in
enclosure(E), enclosure-fertilization(EF) and enclosure-burning(EB) grassland, while
decreased in grazing(G) grassland. In the 0~20 cm soil layer, soil bulk density of G
grassland was significantly higher than the other three types while EF was the lowest.
In the 0~50 cm soil layer, the soil water content increased with soil depth in the four
types of disturbances and tended to be in the order of EB>EF>E>G. In the 0~40 cm soil layer, soil organic carbon, total nitrogen and available potassium all decreased
with soil depth, and total phosphorus decreased with soil depth, while these variables
of EB increased at first and then decreased in the other three types. In the 0~30 cm
soil layer, the order of soil nutrient content tended to be EF>EB>E>G. The nutrient
content of G in 0~10 cm soil layer was significantly lower than the other three types
of disturbances (P<0.01).
4) The organic carbon content and density decreased with soil depth, but the
decreased amount are different among the four disturbances. In the 0~50 cm soil layer,
the order of the soil organic carbon content was EF>EB>E>G. In the 0~50 cm layer,
the order of soil organic carbon density was EF>EB>E>G, while enclosure-fertilized
grassland reached the highest (14.51 kg·m-2), followed by enclosure-burning grassland
(13.86 kg·m-2), fencing grassland (12.27 kg·m-2) and grazing grassland (11.85 kg·m-2).
Grazing can decrease the soil organic carbon density, while fertilization and fencing
have positive effects on the soil organic carbon density.
5) There was a negative correlation relationship between community
productivity and Shanner-Winener index and Simpson index, which supported the
light and root competition hypothesis. Above-ground biomass was positively related
to vegetation coverage, height and soil water content. Soil organic carbon content was
significantly positive correlated with above-ground biomass and total nitrogen in the
0~50 cm soil layer, while it just showed positively relationship with soil water content
in 0~30 cm soil layer. Furthermore, the results showed that soil organic matter was
positively related (P<0.01) to total nitrogen, total phosphorus and available potassium
in all the four types of disturbances, and total nitrogen showed a positive relationship
with total phosphorus and available potassium.
6）Based on the grayness relationship analysis, our results indicated that:
Key Words: typical steppe of Loess region, disturbances, vegetation community
characteristic, soil physicochemical properties, soil organic carbon