Environmental Engineering Reference
In-Depth Information
Brazilian sugarcane is the world's most productive i eld crop, with fresh yields averaging
about 75 t/ha and with a carbohydrate (saccharose) yield of 8 t/ha. Photograph of mature
crop courtesy of Governo do Estado do Espírito Santo.
reoxidation of i xed carbon energizes autotrophic growth and maintenance (that is,
the synthesis of biopolymers from their monomers, the transport of photosynthates
within plants, and the repair of diseased or damaged tissues).
Autotrophic respiration thus forms an indispensable metabolic bridge between
photosynthesis and plant structure and function (Amthor and Baldocchi 2001;
Trumbore 2006). Its relative shares are commonly expressed as the quotient R
A
/GPP
and are usually lowest for some intensively cultivated crops. In primary production
terms, agriculture can be dei ned as an endeavor aimed at maximizing GPP while
minimizing R
A
; this quest is achieved primarily through the selection of high-yielding
cultivars, adequate fertilization, and, if need be, irrigation. R
A
varies widely both
among biomes and ecosystems (as a function of location and climate) and during
