জলবায়ু আদ্রতা ও উদ্ভিদের ভিত্তিতে প্রতিটি বর্গ কে আবার কয়েকটি উপ-বর্গ ভাগ করা হয়েছে । তাহলে মোট উপবর্গের সংখ্যা কটি?
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Answer:
Vegetation type also affects P availability and transformations in soil systems. Within forest systems, different tree species especially influence inorganic and organic P pools. In a coastal Oregon clay loam, a mixed red alder (Albus rubra Bong.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forest contained 65–225% more dissolved, inorganic P than a pure purely Douglas-fir forest (Giardina et al., 1995). Moreover, phosphatase activity was three times greater in the mixed forest than the Douglas-fir forest, suggesting higher rates of P mineralization in the mixed forest (Giardina et al., 1995). These results are consistent with past research that has concluded that alders recycle P at a quicker rate, promote higher microbial activity, and form stronger mycorrhizal associations than Douglas-firs (Giardina et al., 1995). Overall, these characteristics of a red alder increase the bioavailability of P within the soil solution (Malcolm, 1985; Miller et al., 1991). The results of this experiment provide evidence that different tree species influence P fluxes and, thus, P bioavailability within forest soils.
Moreover, tree associations with ectomycorrhizal fungi affect P fractions and transformations in forest soils (Newbery et al., 1988, 1997). A study conducted in P-deficient oxisols and ultisols in the lowland tropical rain forest in Korup National Park in Cameroon compared soil P fractions in forests with high (45–68%) and low (5–15%) abundances of ectomycorrhizal caesalpiniaceous legumes (Newbery et al., 1997). High ectomycorrhizal (HEM) forests had higher total P, microbial P, and labile inorganic P than the low ectomycorrhizal (LEM) forests (Newbery et al., 1997). Furthermore, the HEM forests had a deeper organic rich, surface layer, allowing the accumulation of organic P via immobilization (Newbery et al., 1997). This organic P pool enables more efficient and competitive P turnover by the trees in the HEM forests compared to the LEM forests (Newbery et al., 1997). Mycorrhizal associations, which vary by vegetation type, play an essential role in P availability in certain forests.
In short, tree species can impact P dynamics in forests. Most significantly, tree association with mycorrhizae promotes greater P availability and more efficient P cycling through both immobilization and mineralization. Thus, total P, microbial P, organic P, inorganic P, and phosphatase activity tend to be elevated under trees with mycorrhizal associations.