On the run for water - Root growth of two phreatophytes in the Taklamakan Desert

Desert phreatophytes require extremely fast root growth for a successful establishment We measured the speed of seedling root growth of two phreatophytic plant species, Alhagi sparsifolia and Karelinia caspia, which form dominant or codominant stands around the river oases at the southern fringe of the Taklamakan Desert. As A sparsifolia occurs at sites with deeper groundwater, we expected the roots of this species to reach down more rapidly than those of K caspia. Furthermore, we expected seedlings experiencing no irrigation and low fertilization to have deeper reaching roots than seedlings with irrigation and fertilization. Seeds of both species were sown into 1 and 2 m long tubes in a glasshouse and in a field experiment, respectively. After 16 weeks of growth in the field roots of K. caspia and A. sparsifolia reached down 2 2 m and 1.7 m, respectively. In accordance with a faster growth, K. caspia had a higher water use, which resulted in a faster decrease of water content in the tubes. Species differences in the vertical reach of roots in the glasshouse experiment were comparable to those in the field experiment After 12 weeks without irrigation, A sparsifolia had a higher rooting depth (0.45 m) than with irrigation (0 30 m), while root depths of K caspia showed the opposite pattern with 062 m and 0 72 m, respectively Fertilizing increased total biomass of both species, while low level of fertilization had the tendency to increase the root shoot ratio and the specific root lengths (SRL), most likely a response to acquire nutrients at lower costs. However, plants of K. caspia showed an increase in SLR already after 12 weeks, while it took 16 weeks for A sparsifolia to increase SRL in the low fertilization level. Our results show clearly that both species are able to reach the groundwater table in the river valleys (6 5 m) within a time span of five to six months after germination However, the encountered vegetation pattern is probably not caused by differences in the speed of rooting depth, but might be the result of a higher capability of growing up with sand accumulation of A sparsifolia. As additional irrigation and fertilization did not enhance rooting depth in both species, these factors will have little impact in restoration procedures (C) 2010 Elsevier Ltd All rights reserve

CLONAL STRUCTURE AND GENETIC DIVERSITY OF THREE DESERT PHREATOPHYTES

The objective of this paper was to assess clone sizes of three perennial desert plant species with AFLP markers and to relate them to clonal and genetic diversity and to hydroecology. The study was carried out at the southern rim of the Taklamakan Desert, where sexual regeneration is only possible shortly after rare flooding events, resulting in rarely established cohorts with subsequent extensive vertical growth and horizontal clonal spread. In this environment, repeated seedling establishment is excluded. We expected decreasing clonal and genetic diversity with increasing clone size and increasing distance to the groundwater table and a common response pattern among all study species. Maximum sizes of Populus euphratica and Alhagi sparsifolia clones were 121 ha and 6.1 ha, respectively, while Tamarix ramosissima clones reached a maximum size of only 38 m(2). In P. euphratica and A. sparsifolia, clonal diversity declined with increasing clone size and increasing distance to the groundwater table, while genetic diversity remained unaffected. Tamarix ramosissima differed from the other species because of a much smaller clonality. Clone size and clonal diversity were found to be good proxy variables for clone age. Despite the considerable age of the clones, genetic diversity is maintained in the populations