Hemiptera plant. Phloem sap, which has a higher concentration of sugars and nitrogen, is under positive pressure unlike the more dilute xylem sap. Most of the Sternorrhyncha and a number of Auchenorrhynchan groups feed on phloem. Phloem feeding is common in the Fulgoromorpha, most Cicadellidae and in the Heteroptera. The Typhlocybine Cicadellids specialize in feeding on non-vascular mesophyll tissue of leaves, which is more nutritious than the leaf epidermis. Most Heteroptera also feed on mesophyll tissue where they are more likely to encounter defensive secondary plant metabolites which often leads to the evolution of host specificity. Obligate xylem feeding is a
Tonlé Sap fuel food webs, the Tonlé Sap benefits from the influx. Sediment-bound phosphorus serves as food for phytoplankton through higher plants, and research has shown that the metabolizing of the chemical contributes to food abundance and quality. Internal nutrient cycling, therefore, plays an essential role in productivity of a floodplain. The nutrients bound to suspended sediments are important for the Tonle Sap system, particularly its long-term sustainability. The reversal of the Tonlé Sap River's flow also acts as a safety valve to prevent flooding further downstream. During the dry season (December to April) Tonlé Sap Lake provides around 50 percent of