Effects Of Burrowing Plateau Pika (Ochotona Curzoniae) Densities On Primary Productivity And Soil Resource Characteristics In Alpine Meadow

The relationship between rodents activities, taking the plateau pikas as example,and alpine meadow degraded degree has aroused considerable interest and controversy in recent ecological literstrue.The burrowing rodents in use were investigated in Guoluo Prefecture,Qinghai Province, the important part in source region of Yangtze and Yellow river. Then four different densities sampling sites were established in alpine meadow for current study. This research mainly includes two parts: (1)the effects of different burrowing rodents densities on aboveground vegetation factors mainly included plant diversity and primary productivity from May to October; (2) the effects of different burrowing rodents densities on belowground environment factors mainly included belowground biomass distribution and soil resource characteristics in plant growing season from May to October. Main results and conclusions from the research were summarized as follows:1.Composition of plant population,characteristics of species and variation of plant diversity at different burrowing rodents densities plots:PlotⅠ( AZP) with 3 burrows per 1/16hm2 has 36 kinds of species,Kobresia pygmaea and Kobresia humili are dominent species of theirs population.As same as PlotⅠ, PlotⅡ( LP) with 32 burrows has 30 kinds and Kobresia pygmaea and Poa annua are dominent species.PlotⅢ( MP) with 54 burrows has 27 kinds and Aconitum pendulum is dominent species. PlotⅣ( HP) with 85 burrows has 28 kinds,Potentilla anserina and Potentilla multifida are dominent species.Their average significant value are 0.028,0.0345,0.037 and 0.036 respectively.Species diversity and eveness indexes change with the same as the richness index variation tendency of plant communities, however, the dominance index changes the opposite tendency. When the burrows reaches 54 per 1/16hm2, every indexes decline to the smallest. The relationship between plant coverage,richness index,diversity index,eveness index and burrowing rodents density can be described with equation of y=ax2+bx+c,and the correlation coefficient are 0.96,0.9946,0.9815 and 0.9596 respectively. Similarly these plots aboveground biomass display the same relationship of quadratic equation with such diversity indexes, the correlation coefficient are 0.9347,0.9858,0.8852,0.7 respectively. From the above conclusions it can be considered that the unimodal curve function could elucidate the distribution pattern of such diversity indexes, burrowing rodents densities and theirs aboveground biomass better. 2.Variation and relationship between alpine meadow aboveground biomass, belowground biomass,total biomass and different burrowing rodents densities each other:In plant growing season from May to October the aboveground biomass peak value appears in August or September, and the maximum biomass(g /m2)of four plots are 444.6,135.1,150.7,179.1 respectively. The order of annual average biomass is plotⅠ( AZP), plotⅢ(MP), plotⅣ( HP) and plotⅡ(LP). The minimum value of belowground biomass appears in August, and the minimum biomass(g/m2)of four plots are 5263.9,2830.7,1436.3,2280.2 respectively. The order of annual average belowground biomass is plotⅠ( AZP),plotⅡ( LP), plotⅣ( HP) and plotⅢ(MP). Total biomass variation trend is mainly dominated by belowground biomass for its large possession. The total biomass of plotⅠ(AZP)is significantly higher than others(P<0.01)and the order of annual average is plotⅠ(AZP), plotⅡ(LP), plotⅣ(HP) and plotⅢ(MP),which shows that only aboveground biomass can not reveal the plateau pikas population and its destroied extent.The ratio of belowground and aboveground biomass(R/T), although two both are the annual average or the belowground is the maximum value,indicates that the R/T of plotⅡ( LP)is most and plotⅢ(MP) is least. The R/T ratio order of four plots is plotⅡ( LP), plotⅣ( HP), plotⅠ(AZP) and plotⅢ(MP). The belowground biomass of total biomass proportion is bigger than 95% expcect plotⅢ,and the order is plotⅡ( LP),plotⅣ( HP), plotⅠ( AZP) and plotⅢ(MP).The relationship between aboveground, belowground, total biomass and burrows densities can be simulated by y=ax2+bx+c equation, and the correlation coefficient is from 0.8353 to1.0000. When the burrows density is 54(Ⅲ,MP) the biomass is least. The aboveground and belowground biomass variance analysis indicate that aboveground biomass is more sensitive to both different burrowing rodents densities and plant growing months than to belowground biomass.3.Composition of aboveground plant functional groups(PFGs) and variation of theirs water lose rate at different burrowing rodents densities plots:Every plots plant function group biomass and theirs percentage in growing season indicate the significant difference(P<0.05).With the burrows increasing,the sedges and grasses are decreasing gradually. Simultaneously some likly light and bad palatability forbs appear and the proportion increases.Sedges,grasses and forbs biomass change with unimodal curve in growing season and get the peak value in August or September. But residues biomass has the other way round,which decreases to the minimum in August or September and the peak value appears in May and October.Forage grasses water lose rate in May and October are least and in June is most in growing season. Of others plots, the largest water lose rate appear in July. 4.Net primary productivity at different burrowing rodents densities plots: The difference of net productivity of aboveground, all net productivity of belowground and net productivity of whole community is extremely significant(P<0.01). Net productivity of aboveground in plotⅢ(MP) is least of all,while plotⅠ( AZP) is 273.7 g /m2·a,which is higher 64.72% than plotⅢ. Net productivity of belowground is contrary to aboveground. Net productivity of belowground of every soil layers has obvious spatial distribution characteristics in vertical height. Soil layers of 0～10cm,10～20cm and 20～30cm depth are decreased in turn.5.Distribution characteristics of belowground biomass at different burrowing rodents densities plots:The belowground biomass distributes vertical pattern obviously and with soil depth increasing, the biomass reduces suddenly(P<0.01), which is described as contrary Pyramid pattern. The belowground biomass is distributed at a scale of 0～10 cm, and plant roots are trended together in soil surface layer with burrows increasing, especially in August.The relationship between the annual average belowground biomass in erery layers and soil depths is simulated by exponential equation y=axb(P<0.01) , the correlation coefficient is over 0.95, except that plotⅢ(MP) can be described with power function y=aex in July and August, and the correlation coefficient is over 0.99.Belowground biomass variation trend can be described with"V"model , firstly declines sharply and then rises slowly. Although it has significant difference with burrowing rodents densities. Dead roots change approximately same as living roots variation trend and the minimum value appears in August. The ratio of roots and soil weight in growing season with every soil layers difference is significant(P<0.05).With the burrows increasing,the ratio of roots and soil reduces gradully to plotⅢ( MP), 54 burrows per 1/16hm2, then increases to plotⅣ(HP),85 burrows per 1/16hm2.Generally speaking, with the soil depth deepening,the annual average of ratio of roots and soil weight is decreasing, which can be described with linear equation y=ax+b(P<0.05). As a whole the trend in every soil layers of four plots is plotⅠ( AZP)>plotⅣ( HP)>plotⅡ( LP)>plotⅢ(MP).Also the relationship between ratio of every layers roots and soil and burrowing rodents densities is simulated by quadratic equation y=ax2+bx+c(P<0.01), and the correlation coefficient is from 0.7271 to 0.9959.The ratio of belowground and aboveground biomass varies with burrowing rodents increasing by bimodal curve and reduces to the minimum value of 54 burrows per 1/16hm2(MP).General the burrowing rodents in use lies in the approximate zero density(AZP) or medium density(MP) the ratio reduces to lower and lowest. At the low density(LP)or high density (HP)the ratio ascends to higher and highest in June. 6.Effects of different burrowing rodents densities on soil layers physical factors:Soil temperature changes with soil layer deepening of"V"modle at different burrowing rodents densities plots. The temperarture at 15cm depth is lowest and at 5cm depth it is equal to 25cm depth. Soil moisture,bulk density and pH value have no function relationship directly with burrowing rodents increasing, but has linear correlation with soil layers by y=±ax+b equation.The top soil layer moisture is highest and it decreases with soil layer deepening.The soil moisture of plotⅠ(AZP) is highest and plotⅢ(MP) is lowest of four different plots. Also soil bulk density increases with soil layer deepening for the roots mainly assembles in the first layer and plant peak appears in August. Usually soil reveals reak alkalinity and pH value increases with soil layer deepening, too. PlotⅢ(MP) pH value is more than others, whih is decided by the specific characteristics of heavy degraded meadow.7.Effects of different burrowing rodents densities on soil nutrient variation: Soil nutrient content displays the multiplicity with the seasonal variation at different burrowing rodents densities plots. General the content of SOM,TN,TP,AN and AK decreases with soil layer deepening, 0～10cm>10～20cm>20～30cm.The relationship between every nutrient factors content and burrowing rodents densities is significant difference in 0～10cm layer(P<0.05),while it has no significant difference in the second and the third layers. In plant growing season the most content appears in August or September. The order of SOM content is plotⅠ( AZP),plotⅡ(LP), plotⅣ( HP) and plotⅢ( MP), TN content sequence is plotⅠ( AZP),plotⅡ(LP),plotⅣ(HP) and plotⅢ(MP) of four plots. These two factors content change with"V'modle and theirs minimum values appear at 32 burrows per 1/16hm2(LP). TP content maintains invariable in growing season except for in August and AN content of 0～10cm layer is highest than others layers,but 10～20cm and 20～30cm layers are lowest in August. The seasonal dynamic of AK content of plotⅠ(AZP),Ⅱ( LP) andⅢ( MP) is consistent, reaching maximum in August then decreasing .While plotⅣ(HP) is an exception that the minimum value appears in August. Taking the growth initial and growth boom period as the example, separately in June and in August. The relationship between soil nutrient factors content and soil layers, burrowing rodents densities separately both can be described with the equation of y=ax2+bx+c.With the burrowing rodents increasing soil factors nutrient content is decreasing reversly, but the burrows from 54(MP) to 85(HP) the content climbs up suddenly.The lowest content of every nutrient factors is in plotⅢ( LP) of four plots.8. Establishment of suitable burrowing rodents and population density scope: Fully combinated the vegetation and environment of four different burrowing rodents densities plots, it can be deduced that four plots are non-degraded(AZP), lightly degraded(LP), heavily degraded (MP) and moderately degraded(HP) grassland respectively from vegetation succession. Simultaneously it also can be confirmed that the existing conclusion of moderately degraded grassland having the most rodents popolation. From all of above analysis and deduction that 512 burrows in use per 1hm2 is a suitable value and the plateau pikas population scope is from 70 to 110 per 1hm2 from the investigated burrows coefficient. And the conclusion, rodents activities and theirs harm extent are derivative and signal but aggravates the advancement to alpine meadow degradation and succession phase, therefore, only vegetation partial destruction and spot massive distribution lead to the massive plateau pikas moving into, is summarized of this study.