Plants with high SLA have large thin leaves like maple trees. PNC is the plant nutrient concentration, or the grams of nutrient per grams of total plant dry mass. A small uptake in nutrients can lead to a big increase in new growth. This is a function of N investment in leaves and, specifically, things like Calvin cycle enzymes. Check out figure 35C, p. 285.
Plants can also have a high RGR through high tissue nutrient concentration.
Remember when we looked at resource competition in prairie species, the fast-growing, early successional species had high N concentrations in their tissues. SLA is most important determinant of RGR . By spreading biomass over a large area, plants can absorb more light. Except for viny species like kudzu, a plant needs some structral support in the form of a stem to keep leaves exposed to sunlight. In competitive situations where a plant can get overtopped by a neighbor, having a high SLA is not too useful in the dark.