C₄ grasses in boreal fens: their occurrence in relation to microsite characteristics

Abstract

C₄ plants are rare in cool climates, an ecological pattern attributable to their poor photosynthetic performance at low temperatures relative to C₃ species. However, some C₄ species are able to persist at high latitudes and high elevations, possibly due to the characteristics of the particular microsites they inhabit in these otherwise unfavourable environments. One such species is Muhlenbergia glomerata, which occurs above 60°N in Canada and is found in the atypical C₄ habitat of boreal fens. In this study, we evaluate how microsite features affect the success of M. glomerata in boreal fens. We surveyed 19 populations across northern Ontario during the summers of 1999 and 2000. The ground coverage by woody vegetation was the most important parameter affecting the presence or absence of M. glomerata. Woody plants covered over 50% of the ground area in plots where M. glomerata is absent, but less than 20% where it is present. The minimum light intensity threshold for the presence of the C₄ species was about 32% of full-sunlight at plant height. Surprisingly, in boreal fens M. glomerata was largely restricted to the wetter moss hollows, rather than occurring on the dry hummocks where its greater water use efficiency might have been advantageous. Woody species dominated the hummocks, but were uncommon in the hollows. In these cool northern climates M. glomerata apparently persists because sufficient periods of temperatures favourable to C₄ photosynthesis occur, but this persistence likely requires some factor that suppresses the woody vegetation.

Appendix

Details of the sites used to quantify the characteristics of the microsites which support populations of Muhlenbergia glomerata in Ontario

Populations were considered distinct when a hydrological discontinuity was apparent. Sites are typically named by the township in which they occur. Grid references follow the Universal Transverse Mercator (UTM) system, as indicated on the National Topographic System (NTS) of Canada map series (Natural Resources Canada 1999). Note that the populations on this list represent 19 out of over 200 fens examined for the presence of M. glomerata.

Year	Site	Latitude	Longitude	NTS map (1:50,000)	UTM grid reference	Day of year
1999	Batchawana	46 57	84 33	41 K/15	865 022	196
	Pancake Bay	46 58	84 45	41 K/15	739 041	209
	Pardee	48 08	89 35	52 A/4	070 358	201
	Prairie River	48 48	86 47	42 D/15	157 055	206
	T-Bay NW	48 24	89 18	52 A/6	265 644	202
	T-Bay SW	48 23	89 20	52 A/6	271 640	203
	Mosque	44 58	76 54	31 C/15	506 846	189
	Clarendon	45 00	76 53	31 F/2	507 848	190
2000	Carmichael	49 05	82 00	42 G/1	267 371	185
	Ford	49 02	82 02	42 G/1	248 323	186
	McMillan	49 46	84 40	42 F/15	682 159	191
	McCoig	49 45	84 49	42 F/15	572 146	192
	Lindwest	49 43	87 08	42 E/11	904 063	193
	Wildgoose	49 43	87 09	42 E/11	895 062	194
	Errington	49 41	87 03	42 E/11	966 041	195
	Stedman	49 05	90 41	52 G/2	690 389	197
	Colliver	49 06	90 42	52 G/2	678 403	201
	Fisher	46 56	84 33	41 K/15	862 051	208
	Herrick	46 57	84 38	41 K/15	798 029	210